Just for clarity, I've applied for a job under my agency and the clients wants to hire me and also one of my freelancer. The job that I applied for was a hourly contract, however, we decided that instead of hourly, we'll instead do a fix-priced weekly contract and the other freelancer from my agency will be on a hourly contract. How can I get this setup with the client?
Your client will need to send a Fixed-Price offer for you to accept in order to create a Fixed-Price contract. Your client should be able to hire both of you using the same job post.