Rob - cats are different to dogs when it comes to breeds, their personality will be what it is, as you dont know who the parents are, and even if dad had been a russian blue, it might not have made any difference to their personality. We had a litter brought in last year, the boys came round within a week, and were rehomed within 2, the female (Shadow) was with us for 4 months!!! I agree with Lynn, I would see if your vet will neuter younger than 6 months with them being siblings, and if not, do be careful with them.