So you've put the two obvious solutions out of reach. You can't just leave it to them and let them sort it out. Also, you can't just have the executor sell it and split the money.
Let them choose
You could let the heirs choose whether to keep it or sell it. If they choose to sell it, the estate can handle that for them and divide the money. This would also allow for two to vote to sell and overrule the single keep vote.
A two to one vote is still unfair to the one. So how to allow one person to sell or keep? Assuming sufficient income those who vote keep could take out a mortgage and buy out those who vote sell. If there are additional assets or monies in the estate, those can help reduce the mortgage required too.
This allows for any possible division among the heirs. If all three want to keep, that's easy. All three want to sell, also easy. Two want to keep and one sell? Not so difficult, particularly if the estate has other value than just this asset. One wanting to keep and two to sell is more difficult but may still be possible (depends on the one's income and the asset's value and perhaps profitability). As a backup option, if they can't all agree, you can default back to the sell and divide option. That's probably the fairest way to handle disagreement.
Valuing the asset can be difficult. One method would be to put it on the market for six months at the highest price. If it fails to sell at that price, use the lower valuation. This handles the situation where the one sell vote wants to be bought out at an unreasonably high amount. Another option would be to specify a valuation in the will or to specify an appraiser.
The important part is to explicitly allow this decision to be made before transferring title and to set up the parameters of the decision in the will. And as the other answer suggests, involving the heirs in this up front can allow you to address issues while alive that might be contentious without a referee.