Permanently, this time. XP is no longer with the mother and when contacted, said he wouldn't have the children :( Due to her previous behaviour, it's not likely to be an open type adoption, XMIL was told by a case worker that it's likely they will make sure the DCs are geographically far enough away that it's difficult for her to make contact.
DS doesn't have a relationship with him and I don't think he is even aware that he exists, although he met him, he was very young at the time. It's just sad that he'll have a brother somewhere in the world that he probably won't ever be able to get in touch with.