Commentaire sur Bava Batra 3:4

משלשין ביניהם – each band pays one-third, for they are three bands for the three years (i.e., two plotting/scheming witnesses for each year).

If two testify that he has had the use [of property] during three years and they are found to be false witnesses, they must make full restitution to the owner.
If two [false witnesses] testify of the first year, two of the second, and two of the third, they divide up the costs of restitution between them.
If three brothers testify and another is included with them, they offer three different acts of testimony, but their words count as a single act of testimony when the evidence is proved false.
In mishnah four we learn the consequences of falsely testifying with regards to possession for three years.
According to Deuteronomy 19:19 the punishment for testifying falsely is that punishment which would have been meted out on the defendant. In our mishnah, witnesses falsely testify that a man had three years possession of a field. Had they been telling the truth the field would have changed from belonging to the original owner to belonging to the possessor. In other words, through their testimony they caused a field to transfer from one person to another. In such a case, if they testified falsely, they would have to pay the cost of the field to the original owner. They tried to make him lose a field now they have to pay him the cost of a field.
Section two deals with a scenario where three sets of witnesses testify to possession, each testifying to one year. Together they can establish that he had three years possession and now owns the land. If they were found to be false witnesses they will collectively pay the punishment of paying the original owner the value of the field.
In order to understand section three we must mention that relatives are not allowed to testify together in order to make up the required two or more witnesses. In the case discussed in this section three brothers testified to the possession of the field, each brother to a different year. In addition, one person testified to all three years. In total, two people testified with regards to each year, and no single year was testified to by two brothers. In this case their testimony is accepted as three different testimonies, and therefore we do not have a problem of brothers testifying together. However, if they are lying, it is considered to be one testimony, with regards to making compensation to the original owner. The person who testified to all three years will pay half of the value of the field and the three brothers will together pay half, each brother paying one-sixth.

שלשה אחים – for each year, one brother, and another person with the brother, and that other person testifies with all of them and there three [distinct] testimonies, for what this one testifies, the other did not testify, and therefore, their testimony is valid.

והן עדות אחת – regarding the conviction of false witnesses, if they were found to be refuted, they divide up the cost between them, and they are not made false witnesses until all of them are proved to be false witnesses.