Rope damage for Volsk:
1d4(1) = 1 damage as the rope digs into his forelimbs.
Everyone in the boat can make a Dexterity check to keep hold of the side of the boat as it topples, though you've got disadvantage if your hands are still tied. DC 12.
Coin flip determines whether the boat remains upright after everyone falls out:
1d2(1)The boat steadies itself after being jostled, so everyone can make a DC 11 Athletics check to pull yourself back in (again, disadvantage if your hands are tied). If you made the Dex check to grab the side, then you've got advantage on the check (Note: If you have both advantage and disadvantage, the two cancel each other out).