Is it beneficial to have all members of household under 1 car insurance policy?

Currently my husband, 2 sons, & 1 stepdaughter are all on one car insurance policy,under my name. The kids are adults, 24, 24, & 21. My stepdaughter recently was involved in an accident (her fault). Would it be better for my 2 sons to get their own policy? What is the benefit, if any, of keeping everyone on the same auto policy. Our policy expires November 2. Can I expect an increase in all our premiums?