Looks like you misunderstood me a little bit.
What I wanted to ask is:
Can you create a Wizard or sorcerer as player character, whose familar can open locks and disarmtraps?
I was asking for the OC, because I always had neeshka in my party but sometimes I wanted somebody else
but I had to have her because she is the only npc who can disarm traps and open locks.

In MotB I really love safiya, because I have an powerful mage and an average rouge in my party.
And I wanted to be like this in other campaigns.

In NWN1, a pixie familiar had rogue skills, not sure about NWN2.

But another thing, is opening locks necessary?
I always thought it was, and obviously you get XP and cash, but is there ever anything important that can be only got by rogue skills?

It was an eye opener for me to hear a friend played through Dragon Age Origins without having a rogue in party and missed nothing except some random loot. Even all armor sets and such were always in open containers. Cant say how it was in NWN campaigns.

Maybe I am crazy, but whenever I see a locked thing or a trap i get the desire to open and disarm it.
In NWN, dragon age and drakensang I always had one char with me who could do this.
In baldurs gate 2 I was really sad that the only pure rouge npc leaves me after half of the game
and I need a mage/thief combination.
When bashing things open and finding broken Items, I always feel bad because I might have destroyed
the most powerful item in the game.

But that never happens, does it?

I'm the same, with traps and locks as well. It's actually some kind of compulsion one would benefit getting rid off.
Probably hits the same players who also have the compulsion to haul every sellable item to the nearest merchant.

But really, what's the actual point?
I always end up every RPG with 500 spare potions and about a million in cash,
and does the few thousand XP here or there matter?

The problem there is, the characters have personalities. I found both available thiefs to be utterly infuriating, was compelled to use the first available mage (for obvious reasons). Opinions vary, but that's one of the games where many players actually use the characters they like (as persons, not as representatives of their class).

No, not possible in NWN2. Keep in mind that non-rogues can still learn these skills. If you have the "able learner" feat than any high-intelligence character should be able to keep them at half max ranks. If you keep thieves tools handy that should be able to crack all but the toughest locks and traps. I can't think of anything. Most damage spells (as well as arrows with elemental damage) can be used to destroy locked doors/chests, which will also destroy any traps on them at the same time. Traps on the ground can't be destroyed by spells, but can be discharged by running a summoned creature overtop.

There are a handful of repeatable traps that can't just be discharged and a couple situations where the trap is actually an alarm (thus disarming rather than discharging it allows you to proceed undetected), but there just aren't enough to say the rogue is indispensable. Convenient for sure, but certainly not indispensable.

Storm of Zehir probably makes the best use of the rogue out of any campaign, and its end-game is basically one big playground for the rogue. Curse Song is fricken awesome, and on top of all their other buffs and debuffs they make extraordinary party leaders. I ran a Bard in my first NWN2 OC playthrough and never so much as touched a weapon all campaign.