Nice! Are they eating solid food now? They should be able to, you may have to simulate pecking at the seeds with your fingers but they pick up on it fast.
I suspect that the slow feathering might be some mild malnutrition, so my thoughts are the sooner the better for them to be on adult pigeon...
I think your temps are correct, I wouldn’t go above 85F by day 5. The squabs are so heavily bodied in comparison to pretty much any other baby birds I can think of, that they generate a truly remarkable amount of body heat just by being well fed.
For what it’s worth, by day 15 the parents are...