You split the proceeds equally, but you will likely owe different amounts of capital gains taxes. This is because your basis is most likely different than your uncle's - when you inherited the property at age 7 you inherited it at its market value at that time. If you can find out what that value was, you will then know the basis for your half.
Here's an example to show you what I mean:
Suppose your father and uncle origianlly bought the property for $10K total, splitting the cost equally - their original basis is therefore $5K each.
Some years later your father dies and you inherit his half. Now if at that time the market value of the property had risen to, say, $15K, then the basis for your half is $7,500. This is because the basis for inherited property is "stepped up" to the current market value at the time of his death (or in certain circumstances 6 months after his death).
Now you and your uncle sell the property for $20K, netting you each $10K. You will owe capital gains taxes on $10K - 7.5K = $2.5K, and your uncle will owe capital gains on $10K-$5K = $5K.
So the key is knowing what the market value of the property was at the time you inherited it. I would hope your mother or uncle can tell you what that was. If your father's estate went through probate, there ought to be records around. Or perhaps the executor of his estate would have the records.