Assalaamu alaykum. In the Quran, it is mentioned that Prophet Zakariyya (Zachariah) was made "Kafeel" for Maryam, may Allah be pleased with her. Was there any blood relationship between them; like, was he her brother or uncle or so? May Allah reward you.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

It was narrated that Zakariyya, may Allah exalt his mention, was the husband of Maryam's sister or of her maternal aunt. The evidence for this is the hadeeth which was narrated on the authority of Maalik ibn Sa‘sa‘ah, may Allah be pleased with him, who related that the Prophet, sallallahu ‘alayhi wa sallam, talked to them about the night of Israa' (his Ascension to the Heavens). He said:

"...then he (Jibreel [Gabriel]) ascended to the second heaven and asked for the gate to be opened. It was said, 'Who is it?' He answered, 'Jibreel.' It was said, 'Who is with you?' He said, 'Muhammad.' It was said, 'Has he been called?' He said, 'Yes.' It was said, 'Welcome to him. How excellent his coming is!' When we entered (the second heaven), I saw Yahya (John) and 'Eesa (Jesus) – who are maternal cousins. Jibreel said, 'These are Yahya and 'Eesa, so greet them.' I greeted them, and they returned the greeting and then said, 'Welcome, O pious Brother and pious Prophet!'" [Al-Bukhaari and Muslim]

Please refer to Fat-h Al-Baari and Tafseer At-Tabari in this regard.

Allah knows best.