if you say the brood was very spotty and stuff, the old queen is obviusly failing. now, don't say you saw her brood a month ago and it was ok, it is possible that she starts failing all of a sudden so...
i had 3 queens in a hive.
just take and kill the old one, at least that's what i'd do.
if you don't, there's possibility she'll want to swarm, in best case, she'll be thrown out.