Hi chris, and welcome to pigeon basics, first thing, it is difficult to keep them flying on the natural system, they want to come down and mate,sit eggs etc etc, and if your surrounded by houses and cant force fly them, it could be tricky! Are you feeding them enough? as they wont fly if hungry? is there a reason you have got them on natural? if there coming o.k from training, they should be o.k health wise? do they beat you home every time? sorry for all the questions, but a bit more info will be easier for us to help you.
pete