Feeling excluded by sisters-in-law

My niece is getting married this fall and I just found out that two my sisters-in-law made plans to rent a house together for the weekend, and they didn’t invite my family to join them in the fun. They have done this many times before and I can’t but help feeling left out. They make plans and discuss together and I am never part of the planning or conversations. I feel left out and wish my family was included. I had to reach out to my sister-in-law to ask for the wedding date. We found out from my father and mother-in-law that it was going to be held in another state. I know they do love us, but I can’t help but think they don’t like to hang out with us or they would’ve included us. Should I say something to them? Or ask them why they didn’t include us? How do I feel connected to them when I feel so excluded and hurt? I know Brooke would say just don’t feel excluded. How can I feel this when clearly we aren’t.