If you politely told your family not to pick up the new cat and your dad ignored you anyway, then politely telling them again to leave the cat alone won't work. You will have to be firm about it. Really, you and the cat need time to bond before introducing him to more strangers. I suggest putting him in a bedroom or bathroom while you have visitors until he's adjusted to his new home. I still usually do that with my cats. My girl is 10 and will come out when there are visitors. But she will swat and scratch them if they cross her path wrong or try to pet her. She's been like that since she was a kitten. My 9 year old boy is very shy and hides from other people so it's less stressful for him if I just put him up. He's also been that way since he was a kitten. My 8 (?) year old boy basically doesn't trust any human except for me so he goes in a spare bedroom. He's been that way for the 4 years he's lived with me.