Either owner can force the sale of jointly held property by petitioning the court for a partition by sale. The court will declare what a "reasonable" sale price is & order the sale. The owners end up paying legal fees, court fees, & the sales commission. A court ordered sale is more expensive than a voluntary sale.
Why would you experience a capital gain? Have you owned the property for a long time? When they inherited the land, the new owners got a step up in basis to the lands fair market value at that time. If you really need to spread out the gains, you could consider an owner-financed sale. This spreads out the gains over the life of the mortgage. If you choose this option, you'll need to spend $$ on an experienced real estate attorney.
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.
