64 bits Windows have
completely removed the ability to run 16 bits programs, either DOS or Widows based.
On the other hand
NTDVMx64 is a project based on the leaked Windows source code, from older versions. That's a very big red flag on its stability and reliability of its operation (not to mention of legally and ethically questionable at best), not to mention the lack of capability of being up to date with the Windows modifications from that time to now, should that become necesary. The only thing I can say is, don't use it.
You may want to try to use winevdm instead, which is based on the open source project Wine, a widely used and actively maintained program originally meant to run Windows programs on Linux. While it for sure doesn't ensures 100% correct operation, I would trust it much more rather than someone trying to leverage Microsoft leaks.
Neither are of course completely perfect projects, and such kind of support is an enormous undertake. I tried the Wine-based alternative and it works mostly ok for simple programs, but some games crash or fail in some way or another. This could be the case of the compilers you're trying to run. It ultimately depends on which Windows APIs they're trying to use and which operations are doing, and the support by the emulation engine.
My recommendation would be, enjoy what you have, but don't expect miracles from such an undertake. If you
really need those programs (be the already built or the compilers + source code) and those fails under those emulators, find another way to run them. DOSBox is normally the way for DOS-based programs, and a virtual machine with a 32 (or even 16) bits Windows would be far more reliable than trying to add x16 support to x64 Windows. Specially when trying to run Microsoft software that is known to use "dirty tricks" to increase compatibility, relying often on undocumented features.
