Wash hands regularly. Not just the hand sanitizer. Real soap and water. Watch where you place your hands after touching common surfaces like handrails, doorknobs and kitchen counters. Keep them away from your eyes, nose and mouth.
Do not have toothbrushes in a common cup or drink from a common cup.
Hi-sorry to hear they're all sick. Do the obvious stuff, sanitize when you can. Keep lots of tissue available & a nearby place for them to dispose. Try not sleeping in the same room. Hopefully they all cough/sneeze into their elbows. When you can, air-out the rooms. Do not touch your face, cuz that's how germs enter your body, usually. Hope they feel better.
Afraid there is very little you can do, honestly. You're surrounded by germs, in the air, no matter how much you wash & avoid family members. What I'd suggest is just be prepared for the inevitable - get plenty of sleep, eat well, exercise & stock up on pain reliever & cold medicine/Nyquil, should you need it. (And be very thankful if you don't!)