I am not allowed to do your homework for you.
宿題をしてあげてはいけないよ
Check your class notes or textbook to see the structures you are currently studying, use a dictionary for unknown vocabulary, have a go yourself.
As Jessiさん has said people are more likely to help by correcting your work.
If you want to learn Japanese (or anything else) you only really learn by practising it. There are probably several ways to express these sentences, if someone gives you a construction you aren't studying it'll be more obvious you haven't done the work yourself. I don't know what schools' attitudes to plagiarism are like these days.
That said, you are correct in the first post that ~te wa ikemasen could be used, so could dame desu.
~koto ga dekiru could be used in the positive sentences. Although often about ability it can also convey permission, (or lack of, if negative). However you might be required to more strongly express permission as distinct from ability. (eg. I can drive a car (ability) but I am not allowed because my license has expired. (permission))