Try to remember that their relationship is not yours. Its their path to take and you are just a witness. Your involvement is not necessary or perhaps even wanted.
I'm not sure what you meant by *screening* but its not up to you to screen. It sounds like *veto power* and that is a very tricky position to be in. Doing a tag search for *veto power* will bring up some info on that. It essentially is about the primary partners right to demand their partner not date someone. Newbies tend to us it to make themselves think they have some control. They don't and it often becomes obvious that they just can't demand anything; only work with what is presented to them.
I feel for you. What you are going through is my biggest struggle in poly. I get what you are feeling. It sucks. Hope you find a way to let it go and let them work it out.
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