Quote Quoting flyingron
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NO Jimmy, you own percentages based on what it says on the deed JOINT or TENANTS IN COMMON. If no apportionment of shares are made, you are presumed to have equal shares in ownership. A joint owner can always convert (unilaterally) his interest to tenancy in common.

As far as the IRS is concerned as long as 100% of the gain is apportioned to one or more of the owners they're happy. Note that a gain from someone in the business of flipping is NOT a capital gain, it's ordinary income.
Assuming that the "flip" takes less than a year.