Dear OP,
Yours has been my situation for the last three years. Once my aunt, the "matriarch" of the extended family, a semi-practicing Catholic, died in 2014, that which had been done in secret but never mentioned or acted upon in public was openly "celebrated" at the annual Christmas Eve gathering. There are two "divorced" cousins with "divorced" men living with them, a male "couple," since "married," a lesbian who prefers many "partners," and a daughter of one of the cousins who calls herself a "transgender." There are about a dozen children from age four on up at these gatherings. Fortunately, I was given 10 day's warning that the 2014 event was to be a "coming out" party for Gary and Michael, and a "show of support" for Aimeè, transitioning to "Emile." Gifts and cards were to be for them, not for Christmas, as "none of us believe in it."
The invitation was politely but firmly declined. I attempted an explanation, but was unable to proceed once I uttered the words "morals" and "Catholic." My cousin spewed rash accusations and profanity at me and hung up. There has been no contact between us, myself plus elderly parents, since December 16, 2014---a total split in the family, nearly 30 against three. It's very sad because my mother, in her 90's, is Godmother to several of the cousins who refuse even birthday cards and phone calls. My father is angry and upset at how Mom is treated, and wonders if he is in any way to blame for not speaking to his sister more forcefully as her children were growing up marginal Catholics. My uncle was a non-religious Protestant who didn't honor the promises he made to the priest. At the time of their wedding, my aunt was in her early 30s, living on her own, working at a professional career. My father was 8 years her junior, having joined the service directly after high school. Dad was serving in the Pacific when the Korean War broke out, so he re-enlisted. He didn't find out about the wedding until two months after the fact. I say, "No, Dad, NOT your fault!"
Your situation is admittedly pathetic, but there's no sense in letting it ruin your life in the next world, or in this world! You'll have to make your own traditions and find others with whom to celebrate. It's not easy. I spent most of Christmas 2014 in mourning and was so distraught I was physically ill and missed Mass. 2015 was a little better, but not by much because Dad wasn't well. This year was much better because I planned in advance how the three of us could celebrate the birth of Our Lord in a manner pleasing to Him and suited to the needs of an elderly couple and their 60 year old daughter.
Try this- A week in advance of the times you formerly spent with family, make plans for whomever is left to celebrate with the emphasis on Our Lord, Our Blessed Mother, the angels and saints. It's much easier to come up with wholesome and fun activities with children than with elderly parents in unstable health. As for the explanation as to why you don't visit anymore, answer your children only if they ask, and then only answer what they ask--- no more.
The question of same-sex "marriage" has come up more than once with the 5-7 years old special needs children with whom I work. Since it is a "Christian" agency, I don't have to lie or lose my job. I keep answers brief, simple, and referenced to God's Law and natural law. Even children of low academic ability know that in the animal kingdom, there are mommies, daddies, and babies. Most of all, pray for your wayward family members' conversions.
I'll pray for you and your family.