Issue with overhead tank water pressure - Should I use pressure pump or a normal self priming pump - Please advise

We have an issue with the supply of water to overhead tank (OHT). A row house comprising of 10 tanks and 2 lines run parellel from the under ground tank to all the 10 OHT. Line A serves 5 tanks and Line B serves 5 tanks. Ours is line B and the 5th tank. The pump runs for 45 mins but we get the water at low pressure and only for 15 min.Our tank is the last and at a higher gradient. I presume the water fills all the 4 tank on its way and then supply water to the 5th tank hence the water pressure is low and only for 15min. Please suggest what can be done ,should we use a pressure pump or a normal self priming pump in between the line or increase the dia of the base line (input) to tank and further reduce the vertical line to 1" so  that the pressure is developed and the water is continues for all the 45 min.