I'm going to ask my so to uninvite family for thanksgiving
Why do you not want to see your SO's family?
I don't want them to come over my house, because they always screw things up.
If your SO truly does not mind not inviting family over, then I do not see a problem. However, if they want their family over, you should try and acquiesce. Sometimes the holidays are the only time people see their families.
I don't invite mine for the same reasons.
If you really feel this way you need to let her have time with her family. Next year you can make plans to go visit others and not have them over. That way you can leave when things start getting toxic.