You must provide more info:
1) CPU
2) system memory amount
3) Windows version
4) Game played
I don't know why you require a VM to run those games. Do they not work on newer versions of Windows?
If so, then since it's 32-bit XP you can only allow it 4GB. I'm not sure how VM's work exactly though for this. If it works like NORMAL (without VM) then if you have a 2GB video card you can only use about 1.8GB for the system memory.
I think you can only assign part of the video memory since you are sharing. So if the video card is 2GB, maybe you can assign 1GB and have about 3GB for the system memory as seen by the VM.
(someone else can chime in)
Anyway, you probably want 16GB to run a VM and everything else comfortably but I have to guess since you provided too little info.
*IMPORTANT*
With running so many games at the same time in the background, you are likely going to max out your CPU no matter what you do. Frankly, I'm surprised they would even run properly. Obviously not all playable.
Again, adding physical memory may not help if you have already the maximum assigned to the VM.
I frankly don't understand the point of this even though you've explained. Your system seems to be unusable. Do you get MONEY for this? If not, what do the points get you if you aren't even playing the game?
Trying to keep an open mind, but I just don't get it.