Right - keep it (is it male or female?) isolated from the other cats, at least for a week. The key to avoiding MAJOR confrontations is a slow introduction. I have 4 - two male, two female. Mac (numero uno) came with me when I escaped from Rancho Bizarro (household of six cats and a crazy beagle, and my former husband #2). After six months of freedom, Mac demanded a buddy - so Lucy was adopted and brought home, used the gradual introduction method, and life was good. Then I got a hankering for a tuxedo kitty, and the PTB led me to an adoption clinic where I met Charlie. Ditto the gradual intro. Last but not least, my neighbor moved in with her guy who is allergic to cats, so I opened my big mouth and received Maggie (#4), who looks like one of the Kliban cats.
Your little one should be checked out at the vet asap. Buy some kitten kibble (dry food - forget the wet stuff until later), and plenty of water. Giver him/her her own litter box away from the other cats. Actually, the experts say you should have an equal amount of litter boxes as cats. I tried that for a while, but got tired of cleaning and filling 4 poop boxes, so it's down to two boxes. Life is still good. Give kitty lots of attention and warm fluffy blankets. I think the meowing will end, once she/he feels secure. Question: your Alpha and Beta - are they male or female?
Alpha: Male.
Beta: Female.
As it should be.