Usually when he sleeps he puts one leg in a normal position and the other one slightly away, but as I mentioned when he walks on a rough surface he walks OK but his legs move slightly away from each other.
I tried to put like a rubber band on his legs for about 1 hour, everything was ok but he was sleeping in standing position which broke my heart
I don’t know if he can sleep well while he’s standing
Btw, for how long should I put the brace ? and can I put it along the day and remove it at sleeping time ?
I don't think it really bothers them to stand but that is what it will take to fix it and it is much less of a bother to stand and sleep for a week or so then to be crippled and possibly in pain their whole life. I understand how you feel though. Although caiques don't always stand and sleep they often do and they are made for it. I don't think it is at all uncomfortable. It would be for us but we are designed to lay down and sleep, birds are fully equipped to sleep standing up even without falling off their perch.
I have seen people use rubber bands with a small straw in the middle so they do not get tangle but you have to make sure it is just the right size, you really do not want extra tension from the elasticity of the rubber band and it should be loose around their legs.
I basically make two bracelets out of vet tape (or whatever you can use) and put one on each leg, the upper part of the leg just below the body (not just above the feet). Then you need to connect the two with something that is just long enough to hold the feet in their natural position. You have to keep an eye on it an make sure it is not too tight as they grow. Usually you need it for a week to 10 days. You can remove it an check as needed but you will have to put it back on so I would plan on leaving it at least a week before checking. He would be able to walk with the brace on, even better than he can now.
I have found that it is easiest to make the whole thing first and then attach it to the babies legs. Sorry it's a bit hard to explain.