What to do if a woman wants to start a poly triad relationship, a F-F-M setup?

I'm in a situation where a woman wants to setup, or what I'm guessing to be a long-term poly triad relationship. She's already in a relationship with another woman, should she make all the decisions? She's inviting me or to be involved with her in that way. She's being a bit awkward about it. I'm not refusing her offer. It's a 1st for me also.
What to do if a woman wants to start a poly triad relationship, a F-F-M setup?
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