Here's the issue: "how do I update a split deposit with payee info"

In the Register view, you see the Transactions. If you double-click and Open the DEP, that's a Worksheet. There is not supposed to be a name in the Register view; and putting one here will conflict with the DEP Listing = the contents that are inside the DEP.

Working in the Register view = you bypassed everything to do with Customer names. Don't put Customer names in the Register view. And if you decide to use the DEP worksheet manually as income, you just bypassed everything about Sales and Customer reporting. All you are doing is "some banking."

The way this works better is to use Sales Receipt, for each customer that paid you Rent, listing the Rental Income service item here. Make sure the File Preferences are set to flow the sales receipt funds to Undeposited Funds, or assign them yourself manually using the dropdown for "Deposit To:" and now you have Multiple entries waiting to be deposited. When you make the deposit entry, you select all the info that is Pending to be selected, and now you see one line in the DEP in the Register, and you open it to see the Details. And now you have Customer Sales activity for financial and customer name-based reporting, as well as reporting on Rent.