the smartest thing wouldn't be to get rid of 3 since they are
females and he already has them flowering
also the plants he brings in could mess up the other plants
pest
fungus
or other bad things can be transfered from plant to plant

also the plant he brings in are probably not on the same light cycle
so they will get stressed and he will run the risk of hermi and then
pollinating his whole crop

so i would say finish out this crop then start with a new strain
but hey thats juts my 2 cents