My in-laws know that we are in a custody battle with his ex wife. We have had repeated problems with her and she has costed us thousands in court cost , etc. She continues to show up when his family is in the hospital, at funerals, and such even though she has been ask repeatedly by my husband not to. There has been several things his family knows she has done or said that would upset my husband and instead of choosing to let him know they have kept it quiet. They call it keeping the peace. They don't realize any of her actions can be used against her in court. The one person my husband has been able to rely (or so he thought) up until now was his mother. We recently found out something that she had known about all along and chose not to tell him. When confronted about it she preceded to defend her actions instead of appologizing. She still thinks that she did nothing wrong. While we now know that she has spoken over the phone along with other family members to his ex. They all act like they are cordial to her face but away from her they all talk behind her back. So if she's not really a friend why would they hold information that would only help my husbands child custody case?

She is still his mother and really, most likely, believed she was doing right, whether she was.

It may not be easy to see that when you are so close and understand the repercussions of her/their actions. She will always be the mother of their grandchild and sometimes one can see reality skewed a little in case the custody battle does not end totally in your favour.

These really though, are just guesses as I don't know enough information from your post about the relationship they share, either your husband and his ex wife's or the in-laws and his ex wife. If you would like to provide more information we may be able to help more.

Are you wanting to ask your MIL to be a spy for your custody case ? That's really what it boils down to. They are entitled to have whatever relationship they want with his ex. It is their choice. If they always came running to your husband then soon that relationship would be over. That is a choice for them to make. What information is it that you think they withheld that would make or break the custody case ?