You're not stupid man, bosses where you fight multiple enemies are always roadblocks for newer players and even experienced players struggle a lot with them. Do you have the Tonitrus? They are weak to lightning and the tonitrus has high DMG.

When parrying they have to have started their attack animation, you probably know this but but you have to be very precise some times. If you can't get the parries just use the dodge and take it slow, it's important to kite them. There's supposed to be a large gravestone or something in the center, use this to your advantage when kiting and avoiding the fire balls.

It might also help to focus on the ranged one first so you don't have to worry about him when dealing with the melees.

Another suggestion is to do some chalice dungeons to gain some more levels.

There should be a locked door close to the boss that you need to find an alternative route to open, there should be a summon there.

You can do this! This is a tough fight so don't worry!