We are in a similar situation and the topic came up a lot lately because my husband and I are planing for a child and my other male spouse is living with us right now. I came across the typical structure of a patchwork family where partners separate and find a new partner and children are involved. It works in that case, the new partners become parents as well, why shouldn't it be as healthy for children to have some additional parents without the process of divorce and such?
We decided to just go for it when the time feels right and both men will become a father in our case. If you are interested the discussion about biological vs adopted was on the last page of my blog if I am not mistaken.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.