It will be difficult to take out the enemies outside without alerting them since they’re positioned near each other. You can sneak inside the hotel (make sure to bring Boomer if you want to maintain Stealth) and take out the enemies from the inside. You can also lay down traps around the doorways and stairs in case you make a mistake and the enemies start searching the area for you.
There are two alarm boxes in the area, one is accessible from the kitchen while the other is in an exposed location where most of the cultists are hanging around. If you want to disable the alarm, take out the one in the kitchen first then use a silenced weapon or sniper to take out the other alarm box. If done correctly, the cultists will have no choice but to search for you instead. You can then actively pick them off one by one until the hotel’s totally cleared.