It really depends.
First, how big do you want them? I agree with everyone else, that you should weigh a live bird. Or, you could process a couple of the bigger ones and see how happy you are with the dressed weight. I like mine at least 5-6 lbs, but other people like a smaller bird. There is no wrong answer to this -- it's just what you like.
Second, how are they doing? If your birds are starting to have trouble walking or moving freely, I would start processing sooner, rather than later, for fear that you may start having birds die on you. From the pictures you posted, they don't look particularly heavy and seem to be in good shape, but you would know better than I.