Do Mormons celebrate Thanksgiving, Christmas, Easter? What are their major family holidays?

If the an average person celebrate a particular holiday, your best bet is that Mormons do also. Some individual Mormons may not celebrate a particular holiday, but as a whole they do. Just like every religion, some people fall out of the norm. For example, I had a neighbor who was a Mormon who personally hate Halloween and call it "bad", so he would have a "Fall Festival" and hand out candy. However, I have seen Mormon churches with Halloween parties, so that is not part of there doctrine.

Yes. Mormons celebrate all those holidays and have nothing against them. The Jehovah's Witnesses are the ones who don't celebrate any holidays.

Yes, we celebrate Christmas Day - and Christmas Eve, and the entire season. Some LDS churches have music events open to the public, or Nativity displays. All LDS churches warmly welcome visitors, and anyone who wishes (and believes in it) may partake of the Sacrament (or Communion).

the simple answer is yes. everyone does it differently. i was invited to christmas dinner and thanksgiving a couple of times

if it was up to me, i would build a life size nativity scene