I would say both the acara and sev with the rams would be fine, but then it depends on the individual fish. My acaras were so laid back and extremely peaceful, if anything it was the rams who did the bullying, although it was just in the form of chasing them away if they came to close to their territory.
On the other hand, you can get sev's that wont accept anything else in the tank with them, so its entirely on the fish.
Your best bet would be to get all young so that they grow up together, also if possible, get the rams first, allow them to establish their territory, then the sev, lastly the acara, but not too long in between to allow routines to form for the others.