Here's a bigger picture...
With a small flock, more than one cockbird is usually asking for hardship on your hens... for larger flocks, multiple cockbirds could be kept, depending on their individual personalities... some share duties, some accept a leader and follow suit and some never accept another being dominant... some cockbirds are stellar alertists and protectors, some not so much... those would be the first ones to cut and run and make it to shelter before a single hen does, lol...
Without a cockbird, yes, an alpha hen usually steps up as the matriarch... however, she is rarely alone... hens are more likely to work together than multiple cockbirds... at the least she usually has 1 or 2 betas that will run 3 point guard as well... then there are hens that are just oblivious to everything else around them but food, water and roosting...
All in all, you'll just have to see... as you said, you can always butcher the cockbirds... or if that ends up being more than you are comfortable with, offer them free in your local ad site... because until they mature fully, you won't know if they're good ones or not, or if they're for you or your flock or not...
I have had just a layer flock that did fine without a cockbird... and I have had (still have) cockbirds that hens separated into other areas will do everything to escape just to be with...
All I can say is, it wouldn't hurt to try it and see... cockbirds are great, but not everyones cup of tea... hope this helps and good luck with your flock...
