Yeah, littermate syndrome is a problem.
You need to train them separately, walk them separately and play with them separately. If you're playing with Bob or grooming Bob, Sacha should not have the opportunity to "boss" him. She should be behind a baby gate or in her crate. The same goes for Bob, if Sacha is playing with you, etc., he should be behind a baby gate or in his crate.
You can train Sacha to an extent. You can train her that such behavior earns her a time out away from the fun. Every single time. You also need to reward her for appropriate behavior at the same time.
You need to train them separately, walk them separately and play with them separately. If you're playing with Bob or grooming Bob, Sacha should not have the opportunity to "boss" him. She should be behind a baby gate or in her crate. The same goes for Bob, if Sacha is playing with you, etc., he should be behind a baby gate or in his crate.
You can train Sacha to an extent. You can train her that such behavior earns her a time out away from the fun. Every single time. You also need to reward her for appropriate behavior at the same time.