I just can not seem to beat him, he just drains all my pets health and his hardly budges!

Any advice/tips would be appreciated please!

Do I need to be level 60?

You shouldn't need to be level 60 if your pets are well balanced and equipped. I suggest you put links to your party pets here so people can give you suggestions.

edit: I've looked through your stable and found the pets. Could you tell me what order they're in in your party and what role you use them for? One thing that jumps out to me is that Thorn doesn't have all of his proficiency points allocated. Also, if you can you should replace any disciple gear with gear that boosts specific stats that the sylesti needs. The epic armour you currently have on dove should also be put on Thorn instead because illusionist gear boosts the stats he uses perfectly.

Hey, thanks for replying! I have done some changes based on your advice. When it says "evoker" etc, I never know which one works best, other than the illusionist ones for Thorn, who is shadow and Howl, who is fire. Dove is water.

The party order is: Howl, Dove, Thorn.

I am pretty knew to doing any battling like this, so I have a lot to learn haha :3

I've never used a water type sylesti, so I can't help you there much, but you should definitely swap Thorn to first. The first pet in the party receives the most damage so you shouldn't have a fire type, which is an attacking type. Shadow types are designed to take hits and heal themselves, so just putting thorn first should stop you from being taken down as fast. Did you put the second proficiency point on thorn into health? If not, then when he eventually reaches level 60, if you're still using him, put it there.

For gear:
assasin for earth
evoker for fire (illusionist works as well, but evoker boosts dexterity for more critical hits)
illusionist for dark
myrmidon for air

Again, I've never used water so you'll need someone else's advice on that one.

I have made changes that you have suggested thanks :) I also swapped out dove (water) for Amythyst (earth)

I am unfortunately still going down like a sack of potatoes, I really do not know how I am going to beat this one! :(

Earth probably isn't the best type to add to the party because it's also for tanking and you already have Thorn. I would recommend an air type, but if it's too hard to get one up to the right level don't worry. You don't have to beat the dungeon to continue with the story, so you can always just keep going with the story and come back to the dungeon when you're a higher level.

Id like to add that Assassin gear is for water and illusionist is for light. Usually, for bosses, I go with Shadow-wind-wind or light-wind-wind for max damage, but I believe thats only feasible with max stats. Without max stats, I operated a light-water-wind party, light was healer/tank, water was support, and wind was attack.
Id suggest using light in your party, (and distribute all points to intelligence) since it works as a healer, preventing things from dying.

EDIT: Also, Fire is one of the worst ideas of what to toss against a boss. I would use wind in its place.

I would swap out the fire type, from experience they are not the best against bosses...

Thank you all for your replies!

I will change my fire to a light and add a wind. Im worried as my fire has a health of 5000 and the rest have a lot less than that. It is definitely worth a try though!

All advice is much appreciated!

Glad to help! :D