You and the other 5 beneficiaries will assume the ownership of the promissory note on the sale of the land. You will use the same gross profit % that she was using on her return (split by all 6 beneficiaries) and filed on your return the same way she was reporting it.
Per IRS Publication 559:
Installment obligations. If the decedent sold property using the installment method and you are collecting payments on an installment obligation acquired from the decedent, use the same gross profit percentage the decedent used to figure the part of each payment that represents profit. Include in your income the same profit the decedent would have included had death not occurred. For more information, see Pub. 537, Installment Sales.
Please refer to the following link for additional information:
https://www.irs.gov/pub/irs-pdf/p559.pdf
IRS Publication 559
