board and weight?????

I want to share a board with my son he is 5'6" and 95lbs beginner/intermediate rider and I am 5'5" and 145lbs. Would a 128 Motive be to small? What exactly does the weight range mean? It's so different for different boards the same length?

Or should I go with the 134?

The 128 would be too small for you... If you have to share with that big of weight range then your going to want the 134! A bigger board is always better then a smaller one anyways, and your son will grow into the 134.