Possible threat to Pigeon chick.....help

[Shrap]

New here...

A Pigeon couple, who we let take over our balcony, had one of their kids this morning. There has been a lot of ruccuous with other pigeons coming over, Including this one individual who WILL NOT leave and has even been bugging the father on the nest. He has gotten up to peck at the invader, and even the mother has come down to try to remove it. I even tried to shoo it out by moving it with a lawn chair. It also keeps making squealing noises, that I THOUGHT were the chicks... anyways.. I'm fearing for the new chicks life!!

What should I do?

(Please keep in mind that I am not 100% sure that this intrusive bird isn't the mother..... It is solid dark in colour, where the other two are lighter, with a rainbow shine to them.)