If a single 160HP engine can make an RV scoot along, a twin RV with two 100 to 120 HP engines will result in good performance. Single engine performance? Well what people might not know, twins under 6000lbs only have to demonstrate single engine rate of climb for certification. Demonstrate does not mean positive ROC. You just have to demonstrate it, which can be negative ROC. Yes you can have a zero single engine service celling. It is just the regulations for light twins. Once you get over 6000lbs you have to climb single engine.
In a Jet you lose an engine in high altitude cruise, you start to DRIFT DOWN. You can't hold altitude. Same with a light twin you need to drift down to SE service ceiling. SE operations can extend your range before the ground comes up, but given conditions you may be able to maintain altitude. People think two engines is great. It is great, but with serious limits unless you are in larger heavy twins.
All light twins I flew can climb slightly below say 5000 ft DA. When I say slightly I mean 50 FPM. I can tell you my beloved Piper PA-23-160 (Apache) did well single engine, solo, half fuel sea level conditions. Two people, full 108 gal, baggage, high density altitude, loss of engine means pulling the good engine back and making a forced landing. Trying to fly it would result in loss of control.
You also have to worry about Vmc as I am sure you know. You can have too much power from the standpoint of single engine operations. The whole problem is asymmetric thrust. Reducing that helps control. Also adding more yaw stability helps. Did you consider a bigger Vertical Stab/ rudder or ventral fin? Have you estimated Vmc? Vyse (blue line). I think keeping it light (O200 or Rotax) is goodness. I don't think a Convair is heavy but guessing (forgive me no time to research) it is not lighter than a O200 and Rotax. I know the Convair is claimed to make 100 to 120HP. With non feathering prop you will lose more performance and have even higher Vmc.
https://www.youtube.com/watch?v=GIMVkTk26fw