I get replies to emails on my nexus tablet but they dont appear in my Apple iPad, can you solve this proble.

On the iPad, goto settings, then Mail, contacts, agenda. Then on the right side of the page, add new account. click that and setup the account you want to access.
If you have the account working, be aware if you delete a mail while working n an other device, like tablet or computer, the mail can't be opened on any other device.

Assuming both tablets are set up to access the same email account, go into the setting for that email account on both tablets and make sure they are both set to leave messages on the server. What can happen when accessing the same email account from multiple devices is that the first tablet that checks for new mail (usually done periodically) picks up the message and removes it from the server, then when the next tablet comes along, the message is no longer there so that device does not display it.