What is the possesive form of "ye"?

"Ye" is an archaic pronoun that is a plural form of "you".

The possessive form of "you" is "your". The possessive form of "thou" is "thy" (or "thine" before an adjective).

What is the possessive form of "ye"? Is it just "your"?

In Early Modern English, the nominative (subject) form of the second person plural was ye. The rest of the forms of the second person plural are still in use: you (objective), your (genitive), your (possessive).

"Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and that your fruit should remain: that whatsoever ye shall ask of the Father in my name, he may give it you." (John 15:16 KJV)

Like many other languages, Early Modern English differentiated between singular and plural second person. The singular was thou (nominative), thee (objective), thy/thine (genitive), thine (possessive).

Thine served as a possessive adjective when the noun that followed began with a vowel, much like a/an.

"Thou hast defiled thy sanctuaries by the multitude of thine iniquities" (Ezekiel 28:18 KJV)