Just orthopedic or rheumatologist answer some hypermobile joints from ballet, gymnastics. can these loose joints make the normal joints loose?

Not really: Genetic predisposition , activities and injuries can lead to hypermobility of a joint . A a loose joint above or below a normal joint will protect it from being over stressed at time and if any thing would prevent it from becoming hyper mobile.

Loose joints: Indirectly, you are putting additional stresses on muscles, tendons, ligaments, and joints above a loose joint. If well-trained, you can accommodate for these weaknesses.