hugs to you!! i know you are going through a lot. but i wanted to commend you for keeping it all together...you are doing great taking care of your family, and doing what is best for your children.
in laws can be so foul, cant they? not very nice that they left you out. but since they did, and your husband is not there...maybe you can do something fun just with the kids?
unfortunately what happens a lot of the times with inlaws is that they will side with their blood. since you and your husband dont live together, or things might be "up in the air", they may not include you in things that they normally would have. sucks i know...but it is true...even with the kids. and it really is up to your husband to set that expectation with his family. you know what mean?
you know what i would do if i were you? i'd say fuck it. i would take my kids and have a good time with them...and focus on our little family...and my own personal extended family. you might have relationships with his family, and that is good, but they have shown that they will leave you out. so, to protect my feelings and my kids, i would just keep my distance...and do my own thing with my own kids. nc means no new hurts, you know what i am saying? it will always be ugly when you are separated from your husband...it just will. if you and your h decide to reconcile, live together again, then i am sure things will be different.
but for now, take your babies and do your own thing. forget about his family for now. you see?