I do keep rosys together (pairs or trios) but of the same size for most of the year. It DOES make it hard during feeding time and I have had close calls. I seperate them during feeding into seperate tubs and leave them in for AT LEAST 45 minutes before putting them back together. Even after that length of time I have had them bite and wrap each other up, then I had to put them under running water for about 10 minutes until they seperated.
Next I would HIGHLY suggest NOT accidently/on purpose MIX two seperate localities. I KNOW there are people that create morphs but for the most part Rosy People KEEP their Rosys LOCALITY PURE. If they cannot find each other in the wild they won't go into the tanks together.