My family love to eat sushi which they have once a week ..is this safe ?

Yes, if it is: prepared properly. There can be worms in fish, but if the fish is frozen enough before processing and the food preparation is hygienic, there is not risk. The other issue to keep in mind is that some fish have more mercury than others and you need to check into the source of fish flesh and the type of fish. See this site for info on mercury. http://www.epa.gov/hg/advisories.htm