Nephew doesn't want to invite mom to his birthday party

Apologies for the long spiel ahead, there's a bit of context needed.

​

So my wife (32F) and I (31F) currently have (and have had for roughly two years) custody of our nephew Harvey (13M), who is the son of my twin sister Jen. In an attempt to keep a long story short, Jen completed a court-mandated inpatient rehab program around half a year ago, and has since moved in with her girlfriend Charlotte (33F) and her ex-stepdaughter Ella (7F).

​

Harvey has a... contentious relationship with Charlotte. Charlotte is the sister of Jen's ex-husband (not Harvey's biological father, he's deceased, not getting into that mess) who Jen started having an affair with a couple of years ago just before the breakdown of her marriage. Unfortunately, their family experienced a tragedy, which lead to both Jen and her ex's lives spiraling downwards. Ex is thankfully rotting away in prison now (hence why his sister has custody of his daughter) and he's not really relevant to the issue at hand.

​

In the past Jen has accused us of "buying" Harvey by "spoiling" him (a.k.a treating him the exact same way we treat our own two kids). He's a great kid who has been through a hell of a lot and I don't think it's wrong of us to provide him with the same lifestyle as the rest of our family. Jen (and Charlotte) seem to disagree. They also claim that we are actively discouraging Harvey from reconnecting with them, which is not true. Both my wife and I just want what's best for our nephew, and we'd love for him to reunite with his mom but we also aren't going to force him against his will nor are we willing to put him at risk to do so.

​

Harvey had been having sleepovers at Charlotte's place every so often, but we had to put a stop to that after he came home extremely upset to us one day and he admitted to us that they were making him sleep on a tiny uncomfortable couch, and that Charlotte had been locking his ES cat (whose entire purpose is to help him with nightmares / sleeping) in the bathroom because Ella is allergic. She refuses to give a damn about Harvey's marjiuana allergy though, as she continued to smoke joints while he was there.

​

We had to convince him to even give Jen a call on Mother's Day, as he declined spending the day with her in favour of visting my in-laws, which greatly upset my sister but I eventually managed to calm her down over it.

​

Now after all that, we're on to the particular issue at hand. Harvey's turning 14 at the end of the month, and my wife and I have been planning a party for him (paintball / arcade / food). He gave us a very reasonable guest list. There will be a couple of adults there: myself, my wife and my MIL (potentially FIL too if he can get the day off but that's unlikely) and if any of his friend's parents want to hang around. The paintball place requires at least one adult per team, which will be my wife and MIL.

​

We sat Harvey down yesterday and broached the subject of his mom, Charlotte and Ella while I was finalizing the guest list. He got a little uncomfortable, then said that he didn't want to invite them. He pointed out that Ella is too young for paintball and there won't be any kids her age (our son will be on a playdate) which is a good point. As for Jen and Charlotte, he essentially explained that most of his newer middle school friends don't really know about his situation and he wouldn't want them asking questions about who they are / why they are there / why he lives with his aunts if his mom is around (apparently he told them the reason he lives with us is because she's "not involved").

​

On the one hand, I want to abide by his wishes because it's his birthday after all and I don't want him upset. On the other hand, I'd rather not upset Jen, because she might take it out on Harvey and make things worse for him. Or she'll blow up at us and accuse us of forcing him to exclude them or something. How the hell do I go about dealing with this without making things even worse than they already are?