Do you not have any loot you can trade for potions? There is food in the storage room beside the kitchen, which you can get into if you agree to help the chef. With food you can rest using a bed, haystack or the portable bedroll you can find shortly after you jump down the pit at the start of the game.
You do not need to sound the gong. You can enter the east door, or head north then east to sneak up on the guards. Either way you should be able to attract 2 and mostly finish them off before the other 2 join in.
The act 1 summoning doll can equip a crossbow (the only doll which can use a ranged weapon) and provide support (set it to aggressive mode). Even if upgraded the dolls are not that tough, so keep it behind your main characters.
The healing spell is handy for healing after fights, and can help you conserve potions. It can be used during fights, but you would have to break off and move away in order to have time to heal without exposing yourself to attack.
Once you get past the guards there is a tougher fight. You may want to try entering the BF a few times to look for better equipment and more potions.
The key to the door you can not open can be found past the guards you are having trouble with. The stairs lead out of the citadel, and trigger the one-way trip to the next act. There is a different way to leave act 1, which will give you an experience bonus (see
here).
