Perhaps get the ILs to help? Sometimes having a different face, in my case it is DHs, can shock bubby into going to sleep. He knows he will get away with more if I go in and check him. I do the feed, change his nappy (he is a pooey night sleeper ) and give him cuddles in very dim light. Then I pop him back to bed. If he cries again, which is quite rare unless teething or sick, I get DH to have a go. That way he justs gets a pat and reassurance, rather than me picking him up.

If they are staying with you, why not put them to work? LOL