You're switching to working for the client on your current project? If that's a "buy-out", your employer is presumably getting big $$ when you leave. They won

You're switching to working for the client on your current project? If that's a "buy-out", your employer is presumably getting big $$ when you leave. They won't care if it's written into their contract with the client. Regarding taking coworkers with you, many workplaces have non-solicitation clauses in their employment contact. However, your new employer can buy them out also. Ask your new employer.