Why do insurance company penalize people with good driving records?

My kids who are in their 30s have their own cars and own insurance they live in my home separate apartments they do not use our vehicles but every time they have an accident my insurance on our car goes up i feel this isn't fair they are,nt even on our policy .My son got another insurance and because of others who have lived here had accidents they dropped him I know my sons ex had quite a few accidents while she was here,and I found out she has been using our address, still she has been gone since.our cars are old 99,95,04