Boiler/Radiator and Heating Problem

Last winter, the radiators on the south side of the middle floor of our house worked very well, while those on the north side barely heated up, and there was no consistent heating. We want to find and solve the problem here. Also, in connection with the above, the rooms on the south side of the middle floor are much warmer than anywhere else in the house, and since the radiators are old, they are operated by restricting them, either completely open or completely closed. This causes the rooms to be either too cold or too hot. We need to identify and find solutions to solve this issue as well.