AITAH for not keeping in touch with my Uncle because of his GF?

I, (20F), have an uncle, Sean, (40M), and he has a girlfriend, Tina, (30F). Tina is 9 years older than me. They have a baby, who will be a year old soon. For some context: my sister, (18F) and I have a very close relationship with my grandma and grandpa, (my mom’s parents). We’ve been the only grandchildren on that side of the family until the baby was born. Also before I say this, I’m not a parent. I am just a 20 year old girl who can barely take care of herself.

So, first off, Tina has asked my sister very inappropriate questions. She asked my sister, (who was 17 at the time), if she had sex. I don’t even ask my family that. During Christmas, she made fun of my sister’s boyfriend, and asked my sister, “oh what did you get your boyfriend, other than that pussy?” (Her own words). Mind you, I’m not like that with my family. I understand that she wants to be close with us, but I don’t like that she asked my sister that. As well, she won’t even let my grandparents kiss or even hold their grandchild. I understand that babies are more susceptible to illnesses. I was born one pound, and was in the hospital for the first 100 days of my life, I totally understand.

But, a week ago, my grandparents came over and Tina was very rude to my grandma and grandpa. My grandma wanted to kiss the baby on the cheek and Tina said, “you can’t do that”. My grandpa also held the baby’s finger, and Tina said, “don’t do that you’ll make her sick”. Anyway, I’ve only seen the baby once, and my uncle told us that we can’t go see the baby unless he’s at the house. However, he’s now going to school to become a trucker, so he’ll be home less. Then, about a month ago, we had his 40th surprise party. Tina didn’t want a DJ because of the baby, however, there were like 30 kids under 10. Everyone was having a fun time. And, she was sitting at the table with her mom, her sister and her family. I felt so bad because I feel like my grandma should be there. My grandma is practically my best friend, and she is very close to me and my sister. I want my cousin to have that closeness with my grandma and grandpa.

I feel really bad because my grandma told me and my sister, “it’s ok girls you guys are my granddaughters”. I want to be close with my cousin when she’s older. I want her to know that even though I’m almost 19 years older than her, that if she has questions, that me and my sister are there. I want to babysit her. I want to have a bond with her. But i feel like I can’t. I don’t know what to do. And my uncle doesn’t say anything. He doesn’t speak up. I honestly want to be in contact with my cousin, but I feel like I want to stop keeping in touch with my uncle because of Tina. So, AITAH?