Trying to only rely on companions leads to issues even first time around, optimal parties have 2 tanks and companions only have one and also none of the companions is that great in mechanic, you can get up aloth or durance later, but you will longing for a real expert. Even if they were good at it, they are not meant for the front row, so their spotting is delayed and possibly tanks will still run into a trap.
I love making the best of what i get, currently i am enjoying a potd with companions but they took identical roles, eder is a must, i am really tempted to hire a mechanic, finding pallegina early gives you a tank but later she is a melee dps, kana is not the best tank around, but i guess he is the least bad option, unless the main character is one.
Tweaks i would make to them
Aloth +1 bonus mech, -1 bonus to lore
Durance +2 bonus mech, -1 bonus to lore and athletic
Mother + 3 int -2 per
Pallegina lvl 6 talent superior deflection to keep her more open ended, little deflection never wrong