Your myopia is very small power and you should not worry about this except you should wear glasses for distance, TV, driving etc. Your wife's power is slightly more but this is not pathological and apart from wearing gasses or contact lenses she need not worry either. Myopia means your eyes are slightly bigger than normal and is a sign of intelligent and beautiful people! Power increase slows down once you stop growing physically.
However, this can be inherited and your children may be myopic as well. There is nothing you can do to prevent this. Don't read in poor light specially very small prints and not very close to your eyes either. Balanced food and exercises are helpful as well as you get anti oxidants and good hormones production. This tends to slow down the power increase.