My first thought is that they are Cornish x and have reached the age where they can start having problems due to fast growth. Then I read your thread about only feeding them raw rice. It could be that they are Cornish X and growing fast, but no matter what breed they are, it’s possible that they can’t stand because they are too weak to do so. Rice does not have the nutrients they need, and even if it did, they would need grit to digest it. Being kept in an apartment does not give them a chance to scratch and peck in the dirt (which is a natural grit), or hunt for bugs (which provide extra protein). Without a healthy diet and environment, I don’t think they’ll improve.