Unfortunately not, as the RDP window is either full screen on a single monitor, all monitors, or windowed at a specific size.

What you can do, is run it from a command prompt or shortcut with the parameters to define the window size.

For example, if all of your monitors are 1920x1080, and they're arranged horizontally, the commands for your two windows would be something like this:

Monitors 3,4,5: mstsc.exe /w:5760 /h:1080
Monitors 6,7: mstsc.exe /w:3840 /h:1080

You might need to tweak those values a bit, depending on your monitor layout, taskbar height etc, but that should hopefully point you in the right direction