Property titled to unmarried couple

My parents are separated but not legally. My mother is in the states with her boyfriend and my father has a girlfriend, too. My concern is that my father will buy a land and soon a house will be constructed. I heard that her girlfriend is the principal buyer and my father is just co-buyer,however, I have confirmed through my father that he will pay for the land and house construction and his girlfriend will just share just whatever she can afford, for sure it is just less than 1/4 of the contract price.

What will happen to that property after my father died? Would my mother still have the right in that property since they are not separated? Will my father's girlfriend can transfer the title solely to her name just like that?

We are worried that she might leave my father after she gets what she wants.

Ask your father to have the ratio of their actual shares recorded in the title so there will be no question. his share is still considered conjugal property.