No - if you look at the list of people who can sign it then you will see that they have to be a professional who is a member of professional body. So a Teaching Assistant cannot sign a passport application

If they have a passport, yes

No, they have to be a member of a profession. If you aren't sure what a profession is I suggest you look it up.

Believe can be a teacher but not a TA..Not being rude but they are not very well qualified.

I doubt it as they are not a professional.

Have you looked at the list?