S.A.
How awful for you to have such a severe phobia. I am a bit phobic about it, but certainly not to the extent you are. If I were you, I'd be giving my oldest a daily multivitamin, plus additional Vitamin C and a probiotic supplement. You can find probiotics in a powder form, or as a gummy vitamin. They are also found in yogurt and Kefir. I would be loading him up with that stuff every day. The one year old is a bit young, but as soon as he/she was old enough, I'd be giving that child the same regimen, and then with your newborn once he/she is old enough.
There was another post on here yesterday about Thieves Oil ( a mineral oil) that you can put in a diffuser to purify the air in your home. Thieves Oil is supposed to get rid of bacteria and germs.
My mom swears by spraying your entire house with Lysol, then opening all the windows to air it out. Make sure all surfaces such as doorknobs, remote controls, phones, computer mouse, keypad and the like are sprayed down with Lysol or bleach.
You can't prevent 100% of illnesses, but by you and your family eating a healthy diet, taking supplements, getting the proper amount (or extra) of sleep, and good hand washing you can try to prevent as much as possible.
Best of luck!