Share desktop of A to B with C as the hop. You’ll need access to your own server (C).
Execute on A: (assuming 192.168.1.100 is the ip of machine A)
% ssh -R 3390:192.168.1.100:3389 -l username myserver.com
log in and execute
ping 184.108.40.206 -i 5
to prevent the connection from timing out
Execute on B
% ssh -l username myserver.com -L 3391:localhost:3390
This means that you will be able to connect at localhost:3391 from your home computer and everything will be forwarded to myserver.com:3390.
Point your remote desktop connection to localhost:3391