Doubling the chances of engine failure is not a major concern if you have more than one engine. The impact of asymetric thrust depends how much of it you have. For example the starship design has the engines placed close to the centreline to reduce this impact in a simple manner. Your chances of complete power loss is n squared where n is the chance of failure.
From an engineering perpective are twins are significantly more complex than singles? Unless you are trying to cope with significant yaw issues relating to asymetric thrust. It is simply another engine, the engines are uncoupled. Of course I may be missing something.
Cozy designs have been modified to have two engines in the past without significant reengineering. Their performance may have suffered because the impact of hanging a couple of engines on the wings wasn't fully appreciated but apart from that they were simple cozy variations.
Is it possible to mount two engines on a cannard design in a manner where the yaw produced by a "low, slow and heavy" engine loss won't present significant risks? I suspect that it is possible.