I have three DC and when they were younger it did feel as if we went through phases or tag-teaming it. I can remember being in one isolation room with DC2 waving to DH in another isolation room with DC1. Both kids were spewing and pooing, horrendously ill on IV drips. No sooner than they were discharged, I came down with it and then DH came down with it. That was before DD was even born.
The best advice I have had (after we nearly lost DD to RSV Bronchiolitis as a newborn) is to ensure that hygiene at home is scrupulous. We kept a hospital grade hand disinfectant in all bathrooms and the kitchen for a few years and taught the children how to wash their hands properly.
FWIW once they are all a bit older, it does tail off. We managed to get through the swine flu with only 3/5 of us infected.
I have always had the rule with my children that if you're ill then you stay in your room, away from your siblings. This seems to help prevent it spreading to them all, or at least delays the spread, so only one or two of them are ill at once. Luckily it is rare for me to get ill with anything, which helps enormously.
Doesn't help you at the moment though, sorry. Hope your household is all well again soon.