Hmm sounds like you are blaming the tanks for everything that goes wrong, this is the main reason people dont like playing tanks, cause they get blamed for everything. What exactly cause your party to wipe? It sounds to me like the first two groups you got were overgeared for the content and the last group you got had equal gear to the content.
First Boss - Squid guy and rock adds - For this fight the boss is suppose to be just position the main boss, the DPS is suppose to pick up adds and kill it ASAP. Some tanks will pick up the add to while the DPS kills it, but honestly the DPS should kill the adds pretty quick that no tanking is needed.
Second Boss - The Wall - This is a complete DPS / Healer fight, the fact that you wiped twice has nothing to do with the tank The tank does nothing in this fight but DPS. If your group wipe it is either your fault for not healing though the AOE (boss dont really do much damage though and fairy should be enough to keep them heal) or the DPS's fault for not doing enough DPS. Healer's are also suppose to be in cleric stance to help DPS since you will be just standing there, doing nothing for 95% of the fight.
Third Boss - This will depend on what you wipe from, the tank is suppose to position the boss so that the group wont get hit by the AOE attack. The DPS are suppose to pick up the adds and kill them since they die in like 2 or 3 hits, tank dont have to pick it up. If your group is not hiding from the bosses AOE attack, then tank can't do anything about it except tell you guys to hide. The boss also target either the Healer or one of the DPS with an orb DPS near the end of the fight. If your guys drop the orb on top of the boss, its not the tanks fault.