The adjective form for the pronoun they is their.
The adjective form is the same, answer. Example are 'the answer key', 'an answer expert', 'the answer desk', etc.
no, it can be a verb (to form) and a noun (a form).
This means that for example we have a noun "jealousy" so its adjective form will be "jealous". This is called the adjective form of a noun form.
agonising eg He suffered from agonising pains