Hi,
almost all is in the subject, i started to play with my wife (cleric) and i want to farm a bit and defend our keep from the invader.
I was planning a matter cab but i'm not sure anymore.
I need your wise advice.

The english words for the cabalist specs are Body/Matter/Spirit

The easiest to level with from lvl 20 to 50 is Matter, you just AoE dot and run away.
You should always spend 3 points in spirit with any spec to get the mana refund spell (reclaim pet).

If you have a cleric with you you could try the full spirit spec to level but you either have to use the refund mana pet all the time, or try to have mana regen pots or a mana regen class with you (minstrel or sorc).

At level 50 the body caba is very good when fully buffed, but you won't have access to speed.

Realm defense is funnier and better with the wizard class (ice, earth or fire).
Fire for bolts
Earth for GtAoE
Ice for door PbAoE

Other class nice for realm defense is Scout.

The best farm class in Albion is the Necromancer, but it is not a good RvR class at all.
The second best farm class is the Cabalist which is quite a good RvR class.

So Cabalist is a good choice based on your requirements. The only downside would probably be, that farm-spec (Matter) and RvR-spec (Spirit or Tri-Spec) are different, so you will have to respec inbetween.