Hello,
I am fairly new to Real Estate <1 year and I plan to use this forum to help get some of my answers on certain issues.

I have been providing advice although not officially an agent of seller or buyer to a family friend doing a for sale by owner deal I am woking on getting the buyer financing.
Short story is current owner occupies subject property, and also rents out studio and guest casita out to tenants. THIS IS IN CALIFORNIA. If Escrow closes on June 14th, but 1 renters rent is due on the 1st, and the other's on the 18th, at which point does the rental income belongs to the new Home Buyer? Can a agreement be drafted out between seller and buyer so that the rental incomes starting on July 1st belongs to the new buyer? I hope I was clear.

If you have a current, active real estate license any advice you've been providing has been 'official' whether you mean it to or not.

Typically rental income to a new owner begins on the actual day he becomes the new owner.

In the case you cite with escrow closing on June 14th the new owner would be be due a pro rated share of the June rental income from June 14th til the end of the month.

All income for July should go to the new owner.

If that is the wishes of both the buyer and seller they can draft an agreement stating all incomes go to the new owner on July 1st but absent any such agreement rents would go to the new owner on that date anyway.

You may be confusing the new owner's payment due date with the rent.

Typically mortgage interest is paid 1 month in arrears (behind) so in your scenario the new owner's first payment would typically become due on August 1st. But because there would be interest due from the June 14th closing date and no payment would be made until August the lender would typically collect the June interest at closing.