AITA for telling my FIL we wouldn’t visit his mother with him?

My husband (34) and I (F, 28) were supposed to go visit his grandmother for Christmas. His father, (my father-in-law) works for an airline and told us that he would buy us tickets to fly before Christmas to go see grandma(his mother). As the dates got closer, he kept asking us when we wanted to fly out, making it apparent that he had never bought the tickets. A week before Christmas. He told us that he wasn’t able to get any tickets and that we would have to drive down there. I recently found out that I am pregnant and so my husband and I refused The trip. His father became exceptionally upset with us instead of taking accountability for the fact that he didn’t get us tickets in time. Now they are planning another trip to go see grandma in March. I told my husband that we are not going unless he buys us plane tickets for real this time. Now his father is upset with me because he feels that I am using my pregnancy as an excuse to get out of visiting the family. Am I the asshole for not wanting to be in a car and for 10 hours I have to pee at least every half hour. He’s insisting that if he can’t find a flight that we drive down with him.