@ninjawife - change can feel awkward at first but that doesn't mean it has to be bad. Consider things from their side for a moment, They've been the ones driving the hour and a half for 25 yrs. If they want to stay home and have their own celebration, it's OK. If you don't want to drive there, that's your prerogative. If your aunt is elderly, who knows how many more holidays she'll have? Maybe your cousin is trying to go along with her to make her happy. If you don't want to be around the other extended family members have your SIL and BIL over for Christmas as usual and maybe you can arrange another day for the aunt and cousin to come to a simple dinner or meet at a restaurant somewhere between you.
Last year, there was a mixup with Thanksgiving and our SIL's brother and wife had nowhere to go. I told DD they should come here. They did, and they were delightful guests. This year, they're coming to our family celebration again plus another brother too.
Two years ago, DH and I had nothing to do over NYE. I knew my sister was having her family that weekend for their Christmas. I invited myself. We brought small gifts for everyone. Last year she invited us. Our niece's husband said we're regulars now, no invitation required.
All this to say, sometimes things change and families and gatherings can look different than what we are used to.