I would like to adopt two kittens. What would be the best combination: two males, two females or one male and one female? I already have two female cats: one 6 years old and one 2 years old.

If it were me I would adopt 2 males. Also I would have them neutered as soon as the vet would allow. I think your girls would accept them better. I have 4 cats. 1 male and 3 females and to be honest in the last week or so my girls have been bickering. Also my neighbor has 3 males & 2 foster males and they really get along better than my females. Good Luck