Edit 3 gates to 2 gates...So far in the manga....Lucy got exhausted if she used 3 gates at a time(I assuming you are saying opens 3 gates at a time) so by default lucy will already be exhausted....Not much of a fight.
Chelia can heal her own wounds....I can see her winning this threesome if she can stand still others exhausted & also depends upon Lucy summons(Mention those 2(if all at a time/3 free summon).....I don't think meredy can stand much without those sensory link magic...Her swords can avoided with minimal ease.So it is down to lucy & Chelia