Never breed brothers to sisters. Other combinations are fine: father-to-daughter, mother-to-son, cousins, etc. Until you gain some knowledge as to how genetics works with inbreeding, I would recommend your not breeding closely related pairs.
As mentioned before, mate the same breeds together unless you are trying to get meat rabbits with certain characteristics or you are doing genetic experiments or you don't care about the fate of the offspring. You cannot sell the offsprin