oncahuia.

Headword: 
oncahuia.
Principal English Translation: 

two people divide or share something;

for two people to do something together or share something

James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 228.

Orthographic Variants: 
oncauia, cocahuia
Lockhart’s Nahuatl as Written: 

tic. -cahuia can be with any number; ēxcahuia, for three people to share something; nāuhcahuia, four, etc. Class 3: ōticōncahuihqueh. The construction consists of a number, a -ca- which arranges numbers in groups in a way not yet fully understood, and -huia.

Attestations from sources in English: 

ome + ca + huia (to do something) = two do it, literally

quecahuia, quecahui = three share or divide something

ticoncahuiya = we two shared (something) two ways, or between the two of us

When you see, "we share this, JuanTlayitl" -- the I is implied; in other words, "we share this, Juan and I;" when the verb is plural, the "I" is implied in it because speaker does not name himself.
Robert Haskett and Stephanie Wood's notes from Nahuatl sessions with James Lockhart and subsequent research.

ConCahuisque, yc quiChihuasque tequil = they are to share it and with it do the duties (San Pablo Tepemaxalco, Toluca Valley, 1681)
Caterina Pizzigoni, ed., Testaments of Toluca (Stanford: Stanford University Press and UCLA Latin American Center Publications, 2007), 149.

Attestations from sources in Spanish: 

concahuizque huel nepantla quimocotonizque yn omexti[n] = que lo compartan entre ellos y se divida por mitad para los dos (Cuernavaca, 1597)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 2, Testamentos en náhuatl y castellano del siglo XVI, eds., Teresa Rojas Rabiela, Elsa Leticia Rea López, Constantino Medina Lima (Mexico: Consejo Nacional de Ciencias Tecnología, 1999), 302–303.

cocahuiticate = junto siembran (Ocotelulco, sin fecha)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 1, Testamentos en castellano del siglo XVI y en náhuatl y castellano de Ocotelulco de los siglos XVI y XVII, eds. Teresa Rojas Rabiela, Elsa Leticia Rea López, y Constantino Medina Lima (Mexico: CIESAS, 1999), 214–215.