I think this is a great idea, as it doesn't force me to have to look tenants again, but I'm worried about how do I ensure that the rent I'm charging stays with market rent. 

Try to stay away from the ads and use the search results. 

If rates stay close, you can have the same lender do a full cash out four months or so after the delayed financing and cover your closing costs.

that's a huge red flag as well.just pop on to lendinghome's website they have really good pricingso does lima one.. those are national for real lenders you can compare if someone is cheaper then them then I questions it right off the bat.the only way you can have cheap rates and stay in business is if your like these guys VERY large and make it up in volume.. just be careful don't give out your SS and don't give them any money until you are certain you think they are real.. and they could be.. you have not given any details to help anyone really let you know if they are real or not..

I work full time she’s a stay at home mom.

Person A and Person B would like to sign another year long lease, although Person C is only looking to stay until around June or so, at which point he'll move out and Person A and B will have a new roommate move in, who would be Person D.This is all fine by me.However I'm not sure how to handle the lease renewal. 

I've been on this real estate investor student path for a while now facing the first time investors obstacle course but stayed in line on what was reachable for me on my journey as a student gaining as much knowledge as could in the process in order to succeed.

I’d love to stay in contact with you, and pick your brain every so often.

Until you know that I would stay conservative and use 10% in my analysis.  

I wouldn't have mined waiting 6 months for seasoning if Interest rates were to stay low.