From what I can see, it looks like the thread releasing finger is hitting against the bobbin case housing in 2 spots, I can turn the balance wheel easily (until the finger hits the 2 spots)

http://download.brother.com/welcome/doch000256/l30ls17172020ug03enfrpoes.pdf

Lower bobbin threading Brother

1. Turn the power switch to "o".
2. Raise the needle to its highest position by turning the balance wheel towards you (anti-clockwise) and raise the presser foot lever.
3. Open the shuttle cover behind the extension table on the the front of the machine and remove the bobbin case by pulling its latch towards you and pulling it out of the shuttle race. (fig A).
4. Unwind about 10cm (4") of the thread from a full bobbin and insert it into the bobbin case. (see fig B-1). Pull the trailing thread into the slot then down and to the left, as shown in fig B-2, until it enters the delivery eye under the tension spring (fig B-3).
5. Holding the bobbin case by the latch, fully insert the bobbin case into the shuttle race and release the latch. Make sure the bobbin case finger fits into the notch at the top of the race as shown in fig C.

did you oil moving parts?

Don't know which model you have but most machine bobbins have a metal "flipper" on the front. You need to pull that open with your right thumb and index finger, then insert the bobbincase with the . You might have to wiggle it around (don't let go of the flipper until it is seated and will no longer wiggle). When it has popped into a spot where it will no longer turn, release the flipper.

Bobbin Case Threading and Inserting into Machine

The only part of this video I would contradict is, not stuffing the bobbin thread into the bobbin area. If there is an indentation in the case by the door to put your finger to open the door (like what her machine shows), just hold the thread so it fits through that finger indentation while you close the door. Some machines actually have a little lip by that finger indentation where you lay the thread.

Sounds like a thread jam ! Open bobbin case housing remove bobbin and clean away thread ! Do not force the balance wheel to turn or you will knock out the timing !

To wind a bobbin put the cotton reel on the top pin, take the thread to the left and round the little wheel and back to the bobbin that should be on the winder, wind the thread round a few times to take a grip, release the stop motion in the balance wheel, turn the winder button so the winder moves to the balance wheel and press on the foot control slowly.
When you put the bobbin in the bobbin case make sure it turns anti clockwise.

try this:
Tension:
If the thread is loose on the bottom of the fabric, it's actually the top thread is too loose. Think of 2 little elves playing tug of war in your machine, one on top and one underneath. If you have loops on bottom, the top needs to pull harder (tighten top tension)
Thread test
Test your thread quality to start, thread your machine and LIFT the presser foot (this opens the tension disks). Pull your top thread straight back. If you feel no tension no matter how much thread you pull, your thread is good. If that your machine passes that test, we can go to step 2. If not, try different spool of thread, do the same test until you get a smooth pull (tip: always check your thread this way when you thread your machine)
Step 2:
Pull on your threaded bobbin thread while it’s in the machine. Does it pull smooth and even? If so, go to step 3. If not, try a new bobbin (bobbins get bent or distorted if wound too tight).
Clean thoroughly in the hook and bobbin case area and oil 1-2 drop is all.
Jamming bobbin case:
If it is damaged from turning out of place once, it could have rough spots on it that makes the thread hang on it, and keeps making it turn over and over. Use a finger nail board (fine sanding) and smoothall rough spots. Then reset the bobbin case taking care to put the notch in the bobbin case in alignment with the proper spot in the machine (basically 5 o’clock) when looking at the round area where the bobbin case goes

If it is damaged from turning out of place once, it could have rough spots on it that makes the thread hang on it, and keeps making it turn over and over. Use a finger nail board (fine sanding) and smoothall rough spots. Then reset the bobbin case taking care to put the notch in the bobbin case in alignment with the proper spot in the machine (basically 5 o’clock) when looking at the round area where the bobbin case goes.

Thread test
Test your thread quality to start, thread your machine and LIFT the presser foot (this opens the tension disks). Pull your top thread straight back. If you feel no tension no mater how much thread you pull, your thread is good. If that your machine passes that test, then let me know, we can go to step 2. If not, try different spool of thread, same test until you get a smooth pull (tip: always check your thread this way when you thread your machine)
Step 2:
Pull on your threaded bobbin thread while it’s in the machine. Does it pull smooth and even? If so, go to step 3. If not, try a new bobbin (bobbins get bent or distorted if wound too tight).
Clean thoroughly in the hook and bobbin case area and oil 1-2 drop is all.
Thread knotting on the bobbin can be a lot of things but here's some guidance:
Tension:
If the thread is loose on the bottom of the fabric, it's actually the top thread is too loose. Think of 2 little elves playing tug of war in your machine, one on toip and one underneath. If you have loops on bottom, the top needs to pull harder (tighten top tension)
Jamming bobbin case:
If it is damaged from turning out of place once, it could have rough spots on it that makes the thread hang on it, and keeps making it turn over and over. Use a finger nail board (fine sanding) and smoothall rough spots. Then reset the bobbin case taking care to put the notch in the bobbin case in alignment with the proper spot in the machine (basically 5 o’clock) when looking at the round area where the bobbin case goes.

This is the first and foremost problems that I've found: The bobbin case is packed full of threads. The needle is crooked and must be replaced.

1. The bobbin case has a hook that turns to catch the top thread when the needle is down. The bobbin case assembly must be removed and cleaned totally. The bobbin case assembly is where the bobbin sits. The bobbin case has a black bar that sits on top of it. Listen the forward screw and slide the bar slightly. You will need to move the hand wheel to move the hook to the front-most position. When you have done this the bobbin case will come out easily. Clean it thoroughly and put one drop of oil on the track. This is a lower spot where the bobbin case sits on top of. Before you put the bobbin back in you need to check the tension. It is intended to be even with the top tension.
2. Replace needle and make sure it is in totally and is seated the right direction.

HOPE THIS HELPS

remove the 2 screws in the needle plate. Lift off the plate.Take out the bobbin case and examine it for rough spots or nicks. If there are any it will be necessary to buff them with an emery stick or fine sandpaper. Once the rough spot has has been smoothed, buff it with some very fine steel wool. There must be no rough spots on this bobbin case.Clean all the lint from inside the hook area. Do not pull the wick from the center of the hook. Place the bobbin case in the hook area so that it sits flush and does not bind when the handwheel is turned.Reinstall the needle plate, thread the machine, insert the bobbin and turn the wheel to pick up the bobbin thread and see that it doesn't bind.Test sew