It sounds like she can't deal with jealousy and NRE.
They seem to have unrealistic expectations: that two people can fall in love with a third to exactly the same level, at exactly the same rate. However, it just doesn't work that way.
This couple has a lot of learning to do about polyamory before they'll be ready for what they're trying to accomplish. It's up to you whether you want to be toyed with and taken for granted while they figure that out. I personally wouldn't.
Besides... you're a woman who wants to date a couple? The world is your oyster.
Gralson: my husband (works out of town).
Auto: my girlfriend (lives with her husband Zoffee).
The most dangerous phrase in the English language is "we've always done it this way."