"I wouldn't recommend trying to start engines with it in parallel mode if the starting bank is almost dead"
No problem,
If the almost dead house bank were connected AT start , there would be no bad results.
Many large starters will drag the start voltage down to 10V while cranking and "dead " house batts are seldom below 11.5V , if there not being discarded.
Dead house connected to starts long term,much ungood!