Use the Turpintine that you were given.

Are you sure you have got the turpentine on the sword? if you do, I suggest, leveling up first and then coming back to it.

I was lvl 6 when i did this one. I killed them pretty easily without using the turpentine. I used a sigil stone from one of the Oblivion gates i had beaten. I put it on my helmet and it gave me +7 to blade attacks which put me over the 50 point mark in my strength stat.

I did it at level one.it was my first or second quest,it's really not that hard

Easiest way is to locate them and while crouched put the turpentine on your bow and just sneak shoot them. It will do 3X damage and should kill them.

If you can, use the poison given but try to perform sneak attacks on them and only fight one at a time, block with a shield (it's best) and use fire spells, even the first fire spell given to you will work alright, then after each troll you heal yourself and repair your equipment. It would pay to save it here too, then move onto the next, just remember not to get backed into another troll while fighting one ;)

You can run through the map killing the p-trolls by just slashing at them or you can use the turnipike you can also grab a shield and get your blade and block skill up. after getting to the dead body grab the paint brush and give it to the painter.

You probably just have to level up, but it also depends on both your skills and attributes. If you're having a hard time even with the turpintine, it could also be because of a poor Blade skill or Strength attribute. Or your weapon can be damaged, which will affect its performance.

PS: Shields are a MUST! Before I played Oblivion, I was brought up in the Morrowind way, where shield blocks were random and rather useless. If you are a close-combat fighter, not using a shield is like asking the game to kill you. Even if you DO block (with weapon or shield), if your Block skill is below 25, blocking WILL DRAIN Fatigue, especially if you hold it. Blocking is a must because it reduces damage and stuns attackers breifly. When they stagger after hitting you, slash a couple times (3 at most) and resume blocking. Other than that, avoid fights with multiple foes, big open areas, and make sure to have a LOT of healing potions and repair hammers (10, more for the potions)

You technically don't even have to kill the trolls. The only thing special is you get a rare alchemy ingredient. You can just run through and grab the paintbrush off the body in the back, then run back and give it to the painter.