how can I unseal the broken seals?

I assume you're talking about the forgotten tomb? You may want to look at this thread discussing the forgotten tomb: https://www.sylestia.com/forums/?thread=622

The main thing is that you have to translate the text (I think there are some translations in the thread linked above), and match the right pet to the right skill needed. Your pets need a minimum amount of stat points in order to activate the seal. I heard most people use level 60 pets with all the points in that stat for it to work.

I can't remember much about the boss fight itself, but it'll probably help to go to a lower zone and get your pets to full health and full mana just before you fight the boss, so you can use a finishing blow on him right from the start. Also, use mend whenever your pet's health falls below 75% if you can.


Also, I'll personally recommend reading these two guides if you haven't already, and adjust your team from there if need be:
https://www.sylestia.com/forums/?thread=11101
https://www.sylestia.com/forums/?thread=18775

These will make your team more efficient in battles.