There is a 5 year look-back period for medicaid (different than medicare) so planing to transfer assets to family just before they apply for indigent care insurance will not be acceptable. If your parents are open to it one way it to gift the annual maximum starting now. Another option is to set up an irrevocable trust, which takes the assets out of your parent's hand and thus won't be counted towards total assets. For example, a husband sets up the trust for the benefit of his wife. The wife can draw income from the trust during her life. Although the amount in the trust is removed from the estate, the household doesn’t lose income from the assets. At the wife’s death, the trust and its appreciation pass to heirs free of estate taxes.
Also, and I don't know your situation, but the chance you'll need to sell your farm to pay estate tax is actually very low. If you do need to do that, the cost of long-term care shouldn't really affect the estate. For example, high-end LTC is anywhere from $75-100k per year. The estate tax is about $5.5m. At $100k per year your parents can pay for 55 years of LTC. And private care is world's better than anything they would get on Medicaid. It's not even a comparison.