okay, well me personally, i'm thinking you should all sit down and discuss what things your interested in trying in the bdsm style and then all decide what you would like to take part in and what you would rather be elsewhere while your partners engage in said activity.
past issues taken into account, perhaps you should consider dealving into looking online for all sorts of info into various activities your partners want to engage in, do simply put your mind at ease, find pictures even if you can so you know what to expect so its not such a shock seeing it next time. also perhaps asking your #2 husband to slowly as you'd both like take steps into this, it might help you get more comfortable with things and i get the impression he isn't too into it either, so perhaps the two of you can enjoy some very mild play with your other partners enjoy something more.
as with anyhting else that makes you hesitate, baby steps, let all your partners know this is bothering you and you want reassurance to not be bothered, and more baby steps if your wanting to eventually be okay with some bdsm however light. however, if talking, thinking and trying just in baby steps is really not workign for you, then i'd suggest talkign to your partners again and asking them to do this play elsewhere or on nights when your not there if you simpyl can't move past this. some things are simply hard limits and should be respsected. keep talking, take baby steps, but if its just not for you, ask them to accomadate you somehow and accept that this type of play is not for you.