Praise be to Allah the Lord of the Worlds.
Sexual intercourse that takes place after Talaaq Baa`in of which both spouses are aware is considered Zina (adultery) and one of the grave sins, which require racing to sincere repentance before death.
As for the pregnancy, they must visit a Sharia court or a specialized Mufti to know the Islamic ruling on this matter. And Allah the Almighty Knows Best.