I can't beat the Tsaret and His bandits. No matter how hard I try. If you know how to defeat it, tell me... Thank you in advance for your help!

Hello! I'm not sure if you can have two party slots by then - but unlocking the second may help. Of course, you can always overlevel as well.
If you have only one party slot:
I see Kaen is your highest leveled pet. Her equipment is a bit lacking, but missions and exploration will fix that up. If she is your only pet in the party, you might want to switch her to Shadow element with either a point in Intelligence or Health. A Shadow element will use equipment boosting intelligence and dexterity or agility.

If you can unlock the second party slot - You do this by going to the town plaza in Esior's Haven and clicking the left option and paying a fee of gold. I think it's 10K?
Your two party slots would then be Light in the first and Air in the second. Light's proficiency point(s) should be set in health, as you'll be using a Light as a tank until you get a third slot. Air's points should be set in Strength.

And I see you've got a lvl 69 kelp - be sure to send her on missions to rack up exp - if you level her to 70, you can use her in your party. :)
If you have any more questions, the user Scathreoite is quite knowledgeable in this area. x)
(And a tip - the Q&A forum is a lot more heavily traveled than the battle/arena/zone discussion forums. Any questions posted there get answered super quick lol.)

Thank you! You've helped me a lot!