Lenders will look at all 3 FICOs if applying alone and will take the middle of your 3 FICOs as a basis for approval, rate, etc. If applying with a spouse, the lender will take the lower of the two middle scores as a basis for rate, etc.
I'd aim for as high as possible, but at least 640ish before applying. Higher the better because something might happen during the approval process like higher balances, added baddies, etc., which could knock you out of contention. In other words, don't rest at the industry norm of 620. And the minimum is a YMMV among lenders. Some require more. Some less.
I'd focus on baddies first. Check out the Rebuilding Your Credit board for more info. Pay down any current CCs. Ideally pay all to $0 and get one to report a balance of under 9% of the CL. For the rest, check out the other board. If unpaid, your lender might require you to pay it first before being approved. It depends on the debt.
Finally, a score isn't everything. Lenders will look at past residency payments, income, specific items on your CR, employment, etc.