You and your brother may need to look to speaking with an attorney to draft up a partnership agreement/LLC operating agreement. This document will entail information such as how income/losses will be split, who will manage the partnership etc.
The partnership will be required to file a federal form 1065 and possibly an Ohio 1140.
The partnership will be required to distribute a K-1 to each partner which details each partner's share of income/losses.
The Partner's will then be required to report the K-1 items on their return.
A Florida resident will be required to file a non-resident return with Ohio. Since Florida does not have a state income tax - you will not get a credit for taxes paid to another state.
I would look at loaning him the money (mortgage) as it sounds like you are not going to be in Ohio working. No operating agreements, etc, It would be less liability and I don’t think you would have to pay Ohio state tax.
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