It’s definitely possible to do a Julia embedding which can dynamically load one out of multiple versions of Julia. Loading more than one version at the same time sounds unlikely to work though, at least it’s far beyond my skills.
Unless you’re talking of a huge code base, or you have way more C than Julia skills available, I would absolutely recommend updating the Julia code, one minor version at a time.
If you have just started investigating dynamic linking of Julia, you may find a few things of interest in GitHub - GunnarFarneback/DynamicallyLoadedEmbedding.jl: Embed Julia with dynamical loading of libjulia at runtime.