[annalex]

Yes, the adoption is literally described between the individual disciple and Mary, but the next sentence uses plural: the disciple took Mary "eis ta idia". This shows that the disciple understood the adoption to extend to all disciples who are "of his own".

John
	English: Douay-Rheims	Greek NT: Byzantine/Majority Text (2000)
	John 19
26.	When Jesus therefore had seen his mother and the disciple standing whom he loved, he saith to his mother: Woman, behold thy son.	ιησους ουν ιδων την μητερα και τον μαθητην παρεστωτα ον ηγαπα λεγει τη μητρι αυτου γυναι ιδου ο υιος σου
27.	After that, he saith to the disciple: Behold thy mother. And from that hour, the disciple took her to his own.	ειτα λεγει τω μαθητη ιδου η μητηρ σου και απ εκεινης της ωρας ελαβεν ο μαθητης αυτην εις τα ιδια

It is unfortunate how often Protestant translations obfuscate that passage.

[Cvengr]

The disciple didn’t take her to her own, but to his own.

[Belteshazzar]

“ta idia” is an idiom in Greek, a word which, by chance, derives etymologically from this same Greek word. It simply means his property (it is a NEUTER! plural, and thus could not refer to people) or, in other words, his home. Another word that derives from that same Greek word is “idiot.”