the recommended topology for your scenario would look like the diagrams below.
the first solution separates all subnets with each other using a central firewall. RDP access from PROD to DEV can be implemented using NAT port forwarding or ACL based routing. this approach normally needs a high-end firewall if high performance is required.
if you don't have the multi-interface firewall demanded in the above approach, you may consider the second solution which puts all subnets sequentially. the PROD subnet is the most internal network, and DMZ is the edge to the internet. PROD users can of course access all hosts in DEV (or can be restricted by specific rules) as the DEV subnet is among PROD's route to the internet. the same thing for DMZ.
hope it helps,
bbao