There are many things in this game that re really hard and some that are really easy
The hardest thing for me is trying to defend the hotel in the alpine unrest dlc i usually play solo so maybe make it harder when you are with friends and easier solo
try setting up mines. some are located down stairs in the cellar and some more are outside next to the bear statue. Also if you don’t stand in front of the hotel sometimes they run past me and attack the hotel which I can then shoot them in the back. But it’s a very very hard mission for me too and I barely finished it solo with very little life left on the hotel damage meter.