NAT after NAT should work, port mapping require require to be set on both NAT devices in tandem....like you're doing.
Should work from outside...but are you testing from LAN1 ??
If so either connect to outside address of router 2......
Or add dNAT rule on LAN1 , translating incoming packets on LAN1 with destination PublicIP:3389 into Router2OutsideIP:3389