Very tough situation with the in-laws Hurt, and I wish I had experience to draw from which could help. Fortunately for me my in-laws have been very kind and supportive through out this process. Now I in no way think they will favor me over her but everything has been good to this point.
That being said, do you know if your in-laws know about your wife's affair? If they do then you can politely suggest if she needs financial help that perhaps he might be the one she seeks it from. Then again, that is my passive aggressive side You might just politely disagree with their position and remind them that you are living in the family home and your kids will remain in the family home. If their daughter wants to leave the family or take time out from the family she is free to do so. Or you can just brush it off because ultimately you are not going to convince them of anything.
Hate it for you, and wish you the best...
Me: 42 W: 32 Married 7 years together 8.5 S1: 7 S2:7 Bomb #1: 09-16-13 Recon #1: 11/13 A discovered 04-03-2014 W filed D 05-19-14 but never served me I filed D 12-02-2014 S 05-31-14 Divorced 5-19-16