You have a perfect application for a CSV. You need a CSV, a pressure tank, and a pressure switch for each pump. Set the pressure switch for the 50 GPM pump at 50/70, with the CSV set a to 60. Then set the pressure switch for the 30 GPM pump at 60/80, with the CSV set at 70 PSI. This way the 50 GPM pump will not come on as long as the 30 GPM can keep up with the demand but, it will come on and increase the flow to 80 GPM if needed.
Without the CSV, even with an alternator or "duplexing relay", (witch I never liked) you would need a half dozen big pressure tanks, and the pumps would still cycle on and off all the time.