Theoretically, as long as all parties are consenting it isn't immoral and it could be possible. In practice, multiple-partner relationships almost never go well and descend into bitterness or boredom.
A successful poly relationship would require everyone to more or less be into nothing but casual sex and low-stakes, shallow relationships. It is very difficult to find people who love others very, very much and yet are totally cool with them having other partners. No doubt there are a few people like that here and there, but they are very, VERY rare. So even if you have a successful poly-amorous relationship.... it's really more of a "hey guys who's up for group sex" sort of thing and not really a relationship in the way that most of us want. I strongly doubt it would be very meaningful, deep or long-lasting.
But hey, if that's what people want, go ahead. I'm not going to say it's immoral - you do whatever you want with your body and the bodies of consenting adults. It ain't my business to get involved. If there is a god(s), then your relationship(s) are between you and he/she/it/them. If there isn't a god or gods (as I suspect) then as long as you keep in private and inform everyone you sleep with that you are with 2 or 3 or more other people then that's fine too.
But I'll wager that at the end of the day you won't be happy and you won't have a really cherished relationship with your partners. Or one of you will get super-attached to another one and you'll start feeling jealous or spiteful and the whole thing will end in tears. But who knows, maybe you are fortunate enough to meet EXACTLY the right sort of people who can feel passionately in love with someone while simultaneously feeling no sense jealousy or guilt, then WOW - you must be incredibly lucky and I wish you all the best.