Although Matthew 27:56 and Mark 15:40 only mention three women, John 19:25 mentions a fourth (Jesus' mother). If my understanding is correct, then these passages imply that Jesus and the sons of Zebedee were cousins. This would also partially explain why Jesus was about to put His mother Mary into John's care.
"When Jesus therefore saw His mother, and the disciple whom He loved standing by, He said to His mother, 'Woman, behold your son!'" (John 19:26). Interestingly, Jesus had referred to His mother as "woman" at the beginning of His earthly ministry (cf. 2:4); now He does so again at the end. Jesus, in the midst of great suffering for the world, is not thinking about Himself in the least. It is true love that always has its focus upon helping others!
"Then He said to the disciple, 'Behold your mother!'" (John 19:27). Some wonder why Jesus did not expect His half-brothers to take care of her. The reason probably lies in the fact that they did not believe on Him at that time (cf. 7:5). Jesus wanted to commit His mother to a relative who was a believer, especially one whom He loved and trusted--like John.
"And from that hour that disciple took her to his own home" - John took the responsibility the Lord entrusted to him seriously, and he did so immediately. It should be observed that the fact that Joseph (Mary's husband) is not mentioned or present seems to imply that he was not alive at this time. If he was alive there would have presumably been no need for Jesus to make arrangements for His mother's care.