This continued all day, with times where both jackdaws came in and attacked the doves. When I returned from work, I started recording some of the footage, which went on until early evening. The doves seemed to become weaker and one, in particular, was sitting almost motionless, at the back of the nest box. My intereste started to change to concern, as I felt that the doves were unable to escape and would perish in the box.
I made the decision to climb up to the nest box and open the lower door, allowing them to escape. One dove flew off, after a bit of encouragement, yet I had to physically remove the second one. It flew off, but I have not seen them since. The jackdaws have continued to build their nest in the box.