Unsecured linksys router?

I use unsecured linksys. I have some sites that I don't really want my family members to know I'm looking at. Is it easy for them to see which sites I'm looking at. The linksys router is connected to the main computer in the living room. Which noboy really uses. Is the computer in the living room the main computer that can see other computer sites. Can another wireless computer see your sites too? And is it really easy?