FOR DYMPHNA: I think in paying the estate tax to BIR, the basis of computation is on fair market value indicated on the Tax Declaration at time of death of estate owner and BIR Zonal value, whichever is higher. If for sale, the selling price on the deed of absolute sale, fair market value on Tax Declaration and BIR zonal value, whichever is higher.
You said "I just want to ask, if partition goes through the court, what will be the basis of computation for the monetary value of the properties?" On our experience when my husband and other siblings went to court to partition the property they inherited, the court decision was to partition the property equally among then so that they had it surveyed by a geodetic engineer and had their portion titled in their individual names. You also said "Assuming that heirs don't want to sell the properties except one who wants to get monetary value of his share." On our experience, my husband had it sold after it was titled. Going to court is expensive besides the long period before it is settled (my husband and siblings took 9 years and expenses was shared equally by all). In fact one sibling sold his inheritance right to other sibling at an amount indicated on their agreement, which was even lesser after my husband sold his portion to another person. In short, I think the court would not decide as to monetary value of the property.
I AM NOT A LAWYER BUT JUST AN ORDINARY PERSON SHARING MY OPINION, IDEAS, KNOWLEDGE AND EXPERIENCE THAT MAYBE OF HELP TO YOU.