First time posting here but genuinely curious if I'm the asshole.

My grandmother sadly passed away in December. She was the best grandmother of 13 grandchildren and I lived with her for most of my life before moving to the United States. I visited my home country once a year or so and it was really sad seeing her become more and more fragile. Unfortunately, she passed away before I could visit one more time to say goodbye but oh well. 

In mid-December we heard the news and my immediate family instantly bought tickets to fly there the following day. I had final exams and projects and work but I just had to go and be there for my family, which I never ever see since we moved away. I thought, my grandmother was the reason I even have a family so not going to her funeral was never an option.

We get there and I see an aunt and uncle who live in the same country but a 2-hour flight from where the funeral was. I asked where my cousins were and they said they couldn't come because reasons. Work, whatever. They say this to the person who flew in from a different country to be there.

The thing is, my cousins (4 of them) had been slowly drifting apart from the rest of us. There was no reason for this, just time and distance. But I thought, this is the funeral of their grandmother and not one of them bothered to show up! I was speechless. Over the next few days, some other cousins and I talked about this and they agreed. None of the 4 who didn't show up even sent a text of support or condolences. Absolutely nothing. I was livid. But when I talked to my mom and sister they didn't feel the same way. They said "what if it's the money or time or they maybe have other reasons". Nope. They're a wealthy family and they could've been there for a day. There were no other reasons other that they didn't feel like saying goodbye to our grandma or being there for the rest of us.

Anyway, one of the cousins is getting married this month. I've known about this for several months (not actually from my cousin-I was never formally invited by the bride and groom). The invitations were open "to everyone in the family" which didn't compel me to visit another country to the wedding of who is basically a stranger. I was already on the fence about going but after the lack of cousins at my grandmother's funeral, I never even want to see them again.

So, am I the asshole for being petty and resentful? My mom and sister insist that I should go because they're still family. Well, the one chance they had to prove they were still part of the family, they didn't show up so I don't want to be bothered to celebrate a wedding to which I wasn't even personally invited. They also say I don't know the reasons why they didn't show up to the funeral and that I can't hold a grudge forever but I missed school, work, final exams, and almost had to take an incomplete for my classes but I thought there are important things in life that are worth missing a day or two of work for. 