What Tunes said. It's just like feeding and providing litter boxes for cats; at minimum, 1 of each for each animal. If they have to share, they're more likely to fight.
You will notice both of them eating or only one eating. I have 3 pairs of cagemates all girls and they never fight over food or water. I have one bowl and one bottle for each cage. I do know some members that have had some squabbles and they offer two dishes and two water bottles and that seems to help.
Just keep an eye on both of them and weigh them regularly if you're worried both are not eating.
i have one pair. i use 1 water bottle & 2 food dishes. i also always make sure they each get their own treat and stand there to make sure the other doesnt steal.
if you do get another chin make sure you follow proper quarantine & intro methods.
and weigh them initially and consistantly to make sure that neither is losing weight.
I use large crocks that screw to the side of the cage. I've never had an issue with not sharing. Neither pair like to eat at the same time. but there's plenty so they take turns.