Hi, mflores,
first question from my point of view is, why you want to switch both application parts to the other side in case of a failure in one of them. If only one application fails and switches to the other site, the network connect should do the job like in the local situation. And if really you site is failing, then failures in both applications will toccur and both applications will switch to the other site. So maybe it is not necessary to switch both applications every times. So far so good.
If you want to do this anyway then think about a preonline script to your parent application what checks if the child SG is running on the local site and if not then "hagrp -switch" the child group to the local site. (Take care for bringing online the parent SG on the selected node again with "hagrp -online -nopre <grp> -sys <node>" as last action in this preonline script because the online token is blown by the preonline script.) But keep in mind that every switch to the other site for the parent application then produces a downtime for the child SG!
Hope this helps, let me know if this is going to the wanted direction.
Best regards
Roger