Maybe it'll be easier if you have a better sense of what the dynamic will be between the three of you, which a brief meeting can hardly provide. For instance, the three of you could go out for coffee or a drinks a few times, see if you can be friends and be comfortable. Then, if the vibe is good, it won't be such an unknown quantity to think of the three of you interacting with your other friends. Of course, if the vibe is not so good maybe your fears are justified.
You could also ask for initial guidelines as you feel out your comfort level like "hugs are ok but no kissing either of us when we're all out together and make sure to spend equal time with both of us to the best of your abilities" or something like that.
I was already a part of the same social circle as my gf and her husband, so it didn't come up for us. As for inviting them into the same social circle as me and my bf (which is a largely separate group of people), I would always offer him the option before inviting them to a particular event that's more his thing or his and my thing than just my thing (if that makes sense) since he's more sensitive about being around metamours. But I wouldn't consider it acceptable for anyone involved to insist that one or more persons stay entirely out of a particular social circle... it doesn't seem fair to expect anyone to stay hidden out of sight or miss out on special social events like birthday parties.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.