1. You are a farmer.

Question

2. Thou art a farmer.
(Is #2 the old English forms?)

3. You are farmers.
4. Ye art farmers.
(Is #4 the old English forms?)

5. He is your son.
6. He is thy son.
(Is #6 the old English form? Was 'is' used as a verb at that time?)

Answer 1

Old English is not the appropriate phrase. Old English is a substantially different language from which modern English developed/evolved. What you are calling "old" English is more Elizabethan English, which is modern English, although, as the language changes, some usages have changed.

http://en.wikipedia.org/wiki/Old_English