1. Yes, God is a third person pronoun. 2. "My God bless you" is wrong. "My God blesses you" is correct. However, it is uncommon to attach a possessive pronoun to God so people usually just say "God", not "My God". "My God" gives the impression that you are intentionally highlighting that the God in your religion is not the same God in the other person's religion. You may have been referring to the phrase "May God bless you." Here, "bless" is in the infinitive form (to bless) instead of the simple present form for third person pronouns (i.e. blesses) because of the use of the modal verb "may". However, it is common to hear people say "God bless you" or "God bless". Although they are grammatically wrong if taken just the way they are, they're actually just a shortened version of "May God bless you" and so they are generally accepted as correct. 3. Yestreen is an extremely old word that means "yesterday evening" or "last night". To my understanding, it was commonly used in poems or by the Scottish people in the past, but is not commonly used anymore now.

Cherry and Dan Smith have already answered your questions but I want to add something. Your question should be: Is God referred to in the third person? Be careful with the second one. As has already been stated, this sentence "My God blesses you" is implies that the god I know is not your god. Simply say, "May God bless you." or "May God bless and keep you." or "God bless you." or "God bless." (The last two are short forms of course.) Yestreen... we are all curious to find out where you saw this. I had to search it on Google. http://www.merriam-webster.com/dictionary/yestreen If this opens for you, you can see that Cherry's answer is correct. Merriam is my favorite online dictionary. She hasn't failed me yet. :)

1) I'm not sure what you mean here. Grammatically, we refer to God in the third person. We use the pronouns "he" and "his." Normally we do not capitalize these pronouns but when referring to God some people do. It is a sign of extra respect so it is more common among strong believers. Thus: "I have seen Him in the watch-fires of a hundred circling camps, They have builded Him an altar in the evening dews and damps; I can read His righteous sentence by the dim and flaring lamps: His day is marching on." Christian theology speaks of the "three persons of the Trinity," the Father (the God of the Old Testament), the Son (Jesus Christ), and the Holy Spirit, creator of the universe. 2) I think you've transcribed something incorrectly. The common phrase is "May God bless you." It is a prayer or petition. In some languages it would be in the subjunctive voice. It expresses a wish or a request that God will take care of someone. 3) I'm baffled by "yestreen." Could it possibly be "yessiree?" That's just an emphatic way of saying "yes." "Yes! You bet! I sure will! Yessiree!"