iRule or Pool member monitor

Is there a way to set priority and dependencies for pool member monitoring or through the use of an iRule for the following objective?:

 

 

Objective: With priority group activation (100/0), if either the primary DMZ or internal web/app server fails, the secondary DMZ and internal web/app servers become active. If both web/app servers in the DMZ are taken down for maintenance, the Pool in the internal stays up.

 

 

Load-balancing takes place in our DMZ F5s (via DMZ servers) for thin clients. Separately, but dependently, load-balancing takes place in our internal F5s (via internal servers)for thick clients. Currently, with Priority Group activation, I have setup Pool member monitoring respectively so that the primary web/app DMZ server monitors the primary web/app internal server and vice versa. I do the same for the secondary servers as well. The intent is to satisfy the dependencies that exist with having the primary DMZ server and the internal server conducting LB and in the event of a failure with either primary DMZ server or primary internal server, the secondary DMZ server and secondary internal server take over. This has been tested and it works well. However the challenge is to keep a Pool up if both servers go down in either environment (DMZ or internal). I.E. - If both servers in the DMZ are taken down for maintenance, the Pool in the internal F5s stay up so that users can still access the thick client.