Like you say, you will need DH/DL to match SH/SL of the other end and vice versa. You will also need the pan IDs to match. Another thing to check is the channel (CH). Encryption options will have to be the same too (EE, KY, etc.). The same is true with sleep mode (SM).
It’s probably easiest to start without encryption (EE=0) and sleep mode disabled (SM=0). make sure you have a connection between them and then turn on encryption or sleep.
More to the point, any ‘routing’ between A and B is like magic You do not need to manually update the mesh or routes as they change.
Your node A just needs to be told (via DH/DL) what B’s address is, the DigiMesh node work togather to share info and create a viable path. This is the ‘route discovery’ phase which makes traffic stop for a secodn or two once in a while.