The graphics card is irrelevant. You can accelerate the RDP session using it, but RDP doesnt use the physical display ports at all. Your RDP session is completely independent of the host display hardware for the most part.
You can set the display resolution in the RDP application, and then just full screen it across both of your monitors. You can also just open 2 rdp sessions, one on each monitor, but they wont function as one continuous desktop.
To note though, your performance is likely going to be pretty awful even on a local connection. RDP doesnt like doing two things, rendering massive screens, and rendering ultra high bitrate color. You can try it, but likely you will be disappointed.
