Accumulate documentation, take pictures of these kids when they come over and send the pics and documentation anonymously to CPS.

Honestly, what BM feeds/eats in her home, what jobs she quits, money that is paid (presumably as CO'd CS) and all is none of your business. BM doesn't want you to know, you don't need to know, and I wonder how BM ever knew what was conveyed in your home.

Have the skids previously told you things and had you/DH go back to BM and give her a tongue lashing over it? If so, I can fully understand why BM wants her kids keeping their traps shut.

Of course, it's awful that these kids are in the middle.

So... my advice? Unless you hear something about ABUSE, say nothing about anything you ever hear.

Yes, kids like to "play up" things so that the other parent will think things are awful at the other parents home, and then spend money on the child trying to make up for the other "awful" parent. I see it with my steps -- and my own biological daughter tried it when my ex-husband and I were first split up. She told me that they had "nothing to eat" in their house. I was at first horrified --- then I had an "aha" moment, and I asked her what she meant....turns out there were no "lucky charms" in the house! She also tried to bad mouth her step mom to me several years ago, and I told her that unless her step mom was abusing her that I was not going to let her bad mouth her step mom to me. I told her that it is hard enough to be a step mom, and to give her grace.

Granted since then I've dealt with my ex-h's fiancé (they've been tog. for 8 years), and she is flat nuts -- she has made up stories about me, called me crazy, etc. So I don't defend her anymore!

^^^^Same Here^^^^^^
DH, before me, had his DD's running to him about BM's BF. Of course, the BF turned out to be a loser jerk who really did abuse BM but never laid a hand on the kids. He never would touch their BM with the kids around. Of course, he was affraid of DH }:) Not that DH cared for BM, he just would be angry for someone to do that in front of his kids.
Anyway, DH's DD's would tell him that the BF was evil and mean and BM didn't do this or that or feed them. Same thing, BM didn't let them stay outside playing with their friends at midnight (not bc she was a good mother but because she wanted them in bed so she could get high) or BM didn't have their fav snack in the house. Can't believe I am saying this but in BM's defense she didn't even know their fav snack so how can she stock it. DH had full custody and BM didn't get them regularly.
Well, after DH and I began dating, SD's began to bad mouth me to BM after about six months. Thats about the time I began to lay down some rules. No wearing my clothes, jewlery, make-up. No boys in the house (always a rule from DH). They didn't like it and knew BM hated me so they bashed me to her and she would call DH and scream about how horrible I am. He saw it for what it was, they had done the same crap with the two previous women he had dated, and he laid down the law.
SD's would come and cry to me about what crazy BM was doing, reading me her "suicide" letters, having to have me calm them down and give them advice on how to handle their BM. But I am the bad parent?
Point is, all kids try to play the parents. Parents just have to see thru it and lay down the laws. My ex and I are close, really good friends, and we don't play games with our DD. She knows I will call her BF and catch her lies.