How to claim all rental depreciation from a co-owned rental?

You must have sound substantial economic reason in order to allocate Profit & Loss percentages differently from your ownership percentage.  IRS will not allow you to arbitrarily allocate income or deduction without economic reasons.

Here's an article on partnership allocations.  Coownership of rental properties follows similar rules.

https://www.thetaxadviser.com/issues/2020/aug/partnership-allocations-lacking-substantial-economic-effect.html

In Holdner, T.C. Memo. 2010-175, the Tax Court found that deduction allocations between a father and son farming partnership were not in line with the partners' interests in the partnership. The court proceeded to analyze each of the four factors above and largely concluded that there was "no credible evidence" for the special allocations. "[I]n the absence of substantial proof rebutting the presumption of equality, [taxpayers] had equal interests in partnership income, expenses, and other partnership items." The court presumed that the father and son each owned 50% of the farming partnership, and the taxpayers did not provide sufficient evidence to refute that presumption. As it was determined that the father and son each had a 50% interest in the partnership, the IRS's assessment of substantial-underpayment and accuracy-related penalties was upheld.

If the rental is owned 50/50, then all rental income/expenses are reported 50/50 on each of your tax returns. Now i myself had a situation where I purchased a rental, and the bank required a co-signer on the loan, and also required that co-signer to be on the deed. However, I was the one claiming all rental income/expenses/depreciation since I was the "controlling" authority (for lack of a better word.) Therefore, I was the only one to report all rental income/expenses on my own tax return. Years down the road when I could, I was able to remove my co-signer from the deed with the permission of the lender. However, they remained as co-signer on the loan until I paid it off in full about 8-10 years ago.