Just been reading that they had been trying since they had their son 6 years ago to have another baby but with no luck.
If they feel like this is the way they want to do things, who are we to decide, you cant know how you would feel until you have been trying to get pregnant for 6 years unsuccesfully.
As for their past, they have clearly decided to be together and are for now are both committed enough to want more kids. And even if they don't stay together, they can still raise happy, healthy kids I'm sure.