So sorry this is happening. I would talk to your local pharmacist -- we visit the UK annually and I find that the "chemists" are generally good about advice; they even may talk about homeopathic things to do, but overall, you can't really build immunity to stomach viruses -- they aren't like colds.
Be sure you confine a sick family member to just ONE bathroom. When one of us is sick with anything, especially anything gastrointestinal, that person is confined to one bedroom and one bathroom and we keep the door into the outside world shut! Use santizing wipes all day long on all doorknobs -- that is a very common place for people to pick up viruses. Also use sanitizing wipes on the edges of doors if your family tends to grab the door to open it rather than the knob. Sanitize the phone so you don't get it from your sick husband using it. Truly, it does help -- I do it constantly when someone's ill and I think it helps avoid spreading things, as does isolating the sick person and forbidding others to use the same bathroom (unless you have only one bathroom and it sounds like you have more than one). As someone else noted, wash sheets and pillowcases AND towels daily if needed -- hottest water, strongest detergent, bleach if you can; that too helps prevent the sick person from getting re-infected. Be sure your carpet cleaner is also a disinfectant or even if it looks clean, it could still harbor virus, just as any surface can.
I'd also keep buckets or large bowls (line them with paper towels for easier clean-out) next to everyone. Seriously. Even a hint of hurting stomach means an accompanying receptacle, whatever room you're in, around here. Saves a lot of unsuccessful dashes to the bathrooms and the cleanup that then follows. Disinfect the bowls/trashcans/whatever receptacle you use, if someone vomits in it.
If you have a "mud room" type of sink (not sure what they'd call it in the UK and husband's not here to ask...) use THAT and not the kitchen or bathroom sink to clean out anything with vomit on it! Or else use the bathtub -- easier to spray that down with disinfectant and rinse than to scrub out a kitchen sink repeatedly and maybe forget just once....
I really, really hope things get better. Preventing the spread by doing a ton of annoying but essential stuff like cleaning doorknobs repeatedly is really going to do more than building immunity, at this point.