Hi Nati: before you get confuse due to the swelling number of advice and suggestions (contradictory at most) let me tell you that it is possible to execute an affidavit of waiver of rights favor one of the children since accdg to you, all the heirs are of age and therefore can alienate property.
After the waiver, the child to whom the waiver was made, can now execute an affidavit of self adjudication.
the kind of tax depends how the property was alienated --if by sale (then capital gain tax) and if by donation (donor's tax)
if you need further legal assistance, email me at adpr24242000@yahoo.com
thanks
Atty K.R.