How can I keep my cool around my niece and nephew?

My brother temporarily lives with me (will be until the beginning of next year) so every weekend my niece (12) and nephew (9) come over. I love seeing them but I'm used to them visiting for a few hours then going back home. I can only deal with them for short periods of time, I know... crucify me. My nephew is just so messy and hyper and destructive. They broke our couches from jumping on them, broke my daughters toys, he wipes his hands on the furniture after eating, wears his shoes in the house. Just moved into this place and I want to keep it looking that way.

My niece has a hideous attitude. She tells her mom to shut up, rolls her eyes, calls people stupid or ugly, calls her dad fat and dumb. I refuse to be belittled or disrespected by ANYONE so I shut that shit down real quick but she always tries me. I just want to stop yelling and stressing in my own house. My brother disciplines then but it doesnt last an hour. When I cook I have to cook for them and with their allergies they get special meals, when I clean I clean after them. The noise, the energy, the everything is just so intense. I'm 30wks pregnant and my head is about to explode.