My advice, forget about RDS. It is waaaaay more expensive than anything else. Last time I checked, a normal retail licence of Windows 10 allows VM use. Just remember, one retail licence, one VM.
Performance will be OK on the T40 I think. RAM matters, so have plenty. Maybe at least 4-8 GB per VM. Your remoting protocol is also important to have a decent performance. While normal RDP is OK, it consumes a lot of network bandwidth because it doesn’t compress the video data much. Something like Parsec is way better and it’s free. Downside, you need some video card per VM that supports video encoding.
Anyway. For 2 VMs, no big deal. Just go with RDP. For more, if there is a lot of movement on screen (like a video), RDP will choke because of the network overhead.