Cant get them off the van. is there a snap-ring? rear brake drums

There is no snap ring but rear brake drums often bind to the hub with a rust bond. A trick mechanics use is take a hammer and hit the drum solidly between the studs like you are trying to pound the drum ON.(being careful not to damage them - screw the lug nuts on a couple turns to protect them.) This can actually disturb the rust bond and break it loose. Hitting the drum on the outer edge like you are trying to knock it sideways also helps, but can distort the drum.

Sometimes there a clip over the stud were the lug nut goes you would see it once the wheel is off, try hitting drum with a hammer in front to break free, if drum is loose but wont come all the way off then you will have to unadjust the brake adjuster ,its done through a window on the rear of the backing plate ( backside of were the drum is,) hope this helps.