S.B.
K.,
Here's the thing,
Just because you and your husband are getting devorced does not mean that you have to devorce everyone you have met during your time with your husband.
Keep in mind, you may know how SOME people feel about this separation, but don't jump the gun to quickly to think others are writing you off.
I have had experiences and lost great friends because of break ups and them thinking I had an opinion of them when infact I did not.
And no matter what the circumstances, you may be divorced and perhaps the neices and nephews may not look at you as their aunt anymore, and maybe they do, I don't know, but no matter what they will ALWAYS be your son's cousins. And that's exactly how you have to look at it.
To me family is family, you don't have to be blood related to be family, so there is no reason to disconnect yourself from all of husbands family (if they choose to not treat you badly) If it were me I would just mail out invitations to the cousins and then you aren't going through anyone and putting anyone in the middle of anything and then the parents have the first hand of being invited and can decide rather to come or not.
In the end it boils down to the party is for the kids, sometimes adults have to really be the bigger people, if they choose not to come or choose not to rsvp why they can't make it...well so be it...at least nobody can say that you're keeping your kids away.
Best of luck to you. I hope your son has a fantastic birthday party regardless of who attends :)
S.