The filing of a lawsuit does not create liability. The suit may, and perhaps should, fail. As to suing the other deceased diver, that is not uncommon- all parties alleged to be at fault in any way are generally joined in a law suit. The key in this case is who owed who what duty of due care, and did they breach it. A quick read of limited facts suggests that IF there is any liability, it will be related to providing unsafe equipment, but even that may be a stretch. There are not enough facts known to us by standers to judge the validity of any claims. I take friends, who have their own equipment, diving, and I do not worry about liability for doing so, as an insured pro or even if I was not an inured pro. Dive professionals have a higher standard of care. Equipment renters and loaners create a duty of care. I avoid loaning gear.
Divemaster Dennis
PADI pro, scuba snobs, and , yes, attorney