I'd be careful w/how you approach this. Their parenting style may be totally different from yours. For instance, they may firmly believe in the cry it out method or self soothe.
To me 10-2 does seem like a long time. But are they telling you it's 10-2 or are you there at night and now for sure. Sometimes the actual facts can shift a bit in translation. I am not saying someone is lying, but if the parents said she was crying from 10-2, did they say constantly or would she cry, then doze then cry, etc. Or was it that they didn't get good sleep until 2.
You might glean more insight into their parenting styles, by asking them "how to" questions, like you asking for their opinion. Say you were reading a magazine article that talked about this and you were wondering how many people did this or that. Or you wondered how they dealt with something compared to you own.
If mom is not PPD, then maybe their not hearing her at night. Or maybe baby has her days and nights turned around and wants to be up...and while that's a hard thing to deal with it can be a hard thing to change if you're say working during the day and not with her to help adjust naps, etc.
Since you're the IL then maybe the first step would come easier through your husband. Maybe have a dad's go to the guy's club and he can bring up some of the information and see what kind of response, maybe new dad needs someone to vent too.
that probably doesn't help too much, but I think sometimes it's too easy for us to jump to a wrong conclusion due to lack of information. Some of that is due to all the CSI shows that give us false hope on solving "problems" quickly. We watch these type shows and don't realize how many different answers there could be or how long it does take. Good luck