Noun1 is more Adj1 That [is]Noun2/Adj2[is] confusion

[vinay2]

Which permutations below are correct/incorrect and why?

1. Jill is more beautiful than Jane.
2. Jill is more beautiful than Jane is.
3. Jill is more beautiful than is Jane. (This variation was a correct answer on Princeton practise questions.. and they called #1 incorrect.)
4. Jill is more beautiful than Jim is handsome.

5. Jill is more beautiful than sharp.
6. Jill is more beautiful than is sharp.
7. Jill is more beautiful than she is sharp.

[vinay2]

Any help on this please?