Ok I need some advise from those experienced breeding homing pigeons.

My pigeons won't breed. While not an expert, I am pretty sure I have both male and female pigeons, 4 total. Pictures of the coop below, it is 8ft wide and 5ft high. They get fed regularly, water is always clean. 1 of the pigeons I have had for 16 months, one for 9, and two for 4 months.

Any idea what I can do to encourage breeding?