although i have no experience of your specific application the experience i do have with bmw's and coilovers i would advise against coilovers for normal road use especially if he has a baby as they tend to be far to harsh. same with the spax adjustable kits ive used, even the softest setting was to harsh for road use. ive never used the h+r stuff graceland mentions above but they are highly rated in bmw circles. i personally use the uprated bilsein kit on my bmw for a comfortable but firm ride.