Are we being petty for not inviting family to my son's 16th birthday

My son's birthday is the 25th of December so he was born on Christmas. Every single year we try to have a party I start planning that party in July so we can work around Christmas. I ask everyone what Dates work best for them and we usually have the party the beginning of December. This is after everyone says they ARE coming. Then nobody shows up. Last year hurt the most beautiful I told everyone I'm scheduling a party at an arcade place that had bowling and skating and if they say they can come MAKE SURE YOU CAN COME! because I have to prepay and can't get the money back. Everyone promised and then my son had two friends show up and nobody in the family did because my sister suddenly decided to have a Christmas party and everyone went to that instead. It was embarrassing for him. He told me this year he doesn't want a big party and would actually appreciate it if I didn't invite the family at all because he didn't want to get his hopes up. So we are having his party the second of December and he's having his best friend there along with me, his dad, step mom, and step brothers. My mom found out we were having a party and she asked when it was and I was honest and said he didn't want me to invite you guys because you always bail. He's turning 16 and my own parents have only ever been to his 4th birthday. That's it. 1 birthday in almost 16 years. She was offended and said not everyone has money to buy birthday presents. First off that's funny because she always gets my sister's kids birthday present and Christmas presents but my son is always forgotten but it's not even about that. I told her the whole family always says they're gonna come but then don't and most of the time very few of them give me notice. They just don't show up. My mom went and complained about me and now my sister and aunts and cousins are saying that I'm being petty and teaching my son to be petty and we are supposed to be family. He doesn't want them there. My family puts in 0 effort to be a part of his life and I've tried to get them to be in his life but it's clear they don't care.