We were not able to reproduce it.
Nodes should not connect to all other nodes, generally speaking. Number of connections is limited. But if you run few nodes this should not be an issue.
Can you simulate it with 3 nodes (admin + 2 customers)? Please run multichaind with
-debug=mchn -debug=net
runtime parameters.
If you still see customer nodes are not connected to each other after several seconds, please grant "mine" permission as you suggest, check that nodes are connected, stop all nodes, zip entire data directories for all 3 nodes and send us to multichain.debug@gmail.com.