I mentioned checking out the records just to clarify his situation for you. You had mentioned he continues to call her his wife and that he's putting businesses in her name, etc. It probably wouldn't matter because it's evident that they are together anyway.
It's evident that they both want people to see that they are blissfully happy and if they are remodeling, they want people to see that they are both on board w/having your children over there and want to "appear" as one big happy family. Unfortunately, it may only happen w/your younger children for a while, but the older ones aren't buying into the happily ever after deal w/those two.
Maybe she's the one rushing the "let's have a child together" to ensure that he won't leave her. Clingy, needy women will use any way to keep the man once she's got her claws into him because she knows that he's very vulnerable right now and this is her best shot of keeping him.
I agree w/you that people need to stop sharing info from FB. They think that they are helping, but really they aren't. They aren't the ones walking in your shoes and it's hurtful to receive this kind of news. If this is his sister telling you this stuff, there could be a hidden agenda and she's hoping that this will discourage you and you will just give him everything to get him to go away. Be careful in what you share w/here.
Please, please take care of yourself. Your children need you now more than ever.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.