Polyamory

Hi. I'm a full-time mom to two kids, married for a long time to one partner. Recently, I've become aware that another couple with kids would like to be polyamorous with us--not swinging, which we don't do, but actually long-term grow-old-together family. I'm familiar with polyamory through close friends, but their relationship did not work out and some people argue that it was because of the polyamory. I'm a bit nervous, and hoping for some support and advice. Finding forums is what I do when I need that.