first of all I am not a programmer. It's just not what I am good at. I have an old windows3.1 tts engine called Keynote Gold multimedia application that I would like to decompile and make work on a modern computer system and also on android. If I send someone the dll files could you take a look and see if it can be done, please?
Edited because I misunderstood what kind of software you were talking about.
You don't have to, just run it in a virtual machine such as QEMU, DOSBox or Virtualbox. QEMU probably the best option.
Porting Windows software the way you're suggesting is generally too painful to be realistic, and virtualization provides almost perfect results with little effort.
If it is just a DLL it might be more realistic than a full software package, depending on how complex the code is. Still a lot of work, and if you want it to run on Android you still have to emulate it somehow. Payoff/work ratio very low imho.
You may use WINE to run or integrate a dll into your modern program.