Be safe first. Get all the facts. Demand confidence.
The best thing to do of course is share with your partner(s) the research you've done, and point out the things that scare you about this particular disease. Make sure that they understand your medical experience with what's happened to you already so they know exactly where you're coming from.
Also I highly suggest calling up one of the doctors who have treated you in the past (Maybe one you got along with or felt more comfortable talking to) and tell your doctor that you have multiple partners and want to practice safer sex. Talk to the doctor about the things you've learned in your digging around and they can shed light on what's accurate and what might be exaggerated. They can also help break down the best ways to make sure you stay protected.
Once you're armed with information, flat out tell your partner(s) that extra-quad sexual activities are barred for all of you involved until those outside partners are tested for the virus. If your partner(s) or the outside partner(s) decline to do that, then you have to put your health first, because how sexy and happy can you really feel if you engage with them constantly afraid of infection?
And first and foremost, don't let anyone make you feel rushed. Do not act on requests until you feel safe, and your fears are quelled. There are ways to protect yourself and help you feel confident about your sex-life decisions, but planning and action are key. When you put the work in, the ease that comes afterwards is worth it though, in my honest opinion.