How can I control my emotions with extended family who has no respect for me?

I am currently at my mom house. My aunt family lives 2 hours away and I didn’t want to go to her house. I said no and they begged. The next day they bring their 13 year daughter to stay with us. Mind you I wanted to spend New Years with my mom. Not with extended family!! I want confront my cousin and her family for doing this to me. My mom is stress out with them. Always taking and taking from us. I just want tell her to take that girl n leave. I want scream get out of here. My mom told me not to but I just can’t sit straight. This is such a low blow. They couldn’t respect my wishes to be alone with mom. My cousin might come tomorrow and I’ll pick up a fight. I just can’t hold it in anymore. It’s not right.
How can I control my emotions with extended family who has no respect for me?
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