Not sure the watchtower is able to access commitment transactions unless a breach is detected. I run an lnd tower and a teos tower and let me just say, it's damn near impossible to understand much of anything that's being stored and it's a MASSIVE amount of info. Very gobbledygook, if you know what I mean. Easiest just to take the seeds from each dead node and use those to sign a transaction that splits the funds between the two parties.

Basically one node creates a psbt with one signature that has the split to the two destinations. Then the psbt is sent to the other party to sign and broadcast after reviewing the proposed split.