If I'm the DM, here's what I do. Get the PCs to contact the mother again, via their Speak with Dead spell or other divinations. Go with Vincent being an evil, evil bastard. The child is extremely important. The King *must* know the truth about this child! For some reason that any DM worth his salt can sort out...
Unfortunately, the King has just declared the PCs outlaws, and all his men are gunning for them. Except for the other Arbiter, but he can't help them directly without risking the same fate.
Instant awesome.
...The atonement is doing whatever the frack is necessary to protect the child and see to it that he does not fall into the wrong hands. This *must* cost the PCs everything. They should lose all their non-portable wealth. Their families are thrown in prison and killed. Anyone who helps them is an outlaw. Their old friends turn on them. And most importantly NONE OF THE MAGIC SHOPS WILL SELL TO THEM! ZOMGWTFBBQ!