The Austronesian Comparative Dictionary

*baisan co-parent-in-law, the kinship tie between the parents of a married couple

PWMP baisan co-parent-in-law, the kinship tie between the parents of a married couple

WMP
Tagalog baysán a parent of the spouse of one's offspring; the relation between parents of a married couple
Acehnese bisan the relationship of persons whose children have intermarried (the of the bride are thus the consanguineal kin of her husband)
Melanau (Mukah) bisan son-in-law, daughter-in-law
Simalur bisan-bisan parents-in-law
Karo Batak turaŋ bésan an affectionate term for the mother of one's children; term used between brother and sister, and also between husband and wife
bésan the 'affinal', not true brother or sister; reciprocal term used between the parents of a man and the parents of his wife
Malay bésan the relationship of persons whose children have intermarried
Rejang bisan relationship of parents whose children are married to each other
Sundanese be-besan-an (of two fathers or mothers) to stand or come to be in such a relationship to one another
bésan reciprocal term used between two fathers or mothers whose children have married: co-parent-in-law
Javanese bésan parent(s)-in-law of one's child

PWMP baisan-an become a co-parent-in-law (?)

WMP
Tagalog baysan-an betrothal party held by parents of bride and groom
Javanese bésan-an to become mutual parents-in-law