Aneka Kodi Namaskarams of Adiyen Srinivasan Pranesh.
Understanding from my little brain. I did have this question in mind several times. In olden days, the stages of life as per Vedas were Brahmachary, Grihasta, Vanaprasta and Sanyasa. Sanyasa is not leaving wife and family but detachment from family life in the mind level, which can be practiced along with wife.
We can state many examples from Vedic period like, Vasishtar-Arundhati, Gowthamar-Ahalya etc. Even Janaka Maharaja was a great gnani. Though he was a king, he lived like a sanyasi with wife.
However, leaving the wife to practice Sanyasa after marriage is the one mostly followed in Kailyuga.
This may be because, the life of man of Kaliyuga is short unlike man lived several thousand years in former yugas and hence a dedicated life to spread dharma is required. Further, wife of Kaliyuga may not co-operate like wife in Vedic period as everyone are desire filled and may not match our frequency.
Mostly in case of Acharyas, Sanyasa is taken after consent from God or Acharyan. If one receives consent of God, then nothing is bigger than this. However, we ourselves shall not assume that Sanyasa is correct for ourselves and leave wife without a reason.
In case of Bagavad Ramanujar, he took Sanyasa only after consent from Shri Varadharaja Swamy. His wife was also not co-operative in spreading dharma and was attached to caste sentiments. Further Bagavad Ramanujar was born to become an Acharya. That is the purpose of his life.
In case of Shri Raghavendra Swamy, he was not convinced by his Guru’s words as he was concerned about permission of his wife. Lordess Saraswathy appeared in front of him and said, he was Prahalatha and Vyasaraja Theerthar in previous births and ordered him to accept Sanyasa.
In genuine cases of Sanyasa as i understand, Sanyasa has been accepted only after consent of God or an Acharyan but no one took Sanyasa just because they thought to do so….
In my understanding, one may practice Sanyasa along with wife, if wife is co-operative to our thoughts. Such a dharma patni is a boon given by God. In cases, we may receive order from God or Acharya to accept Sanyasa which would be a special case if it is purpose of one’s birth.
To accept Sanyasa before marriage, a great Vairagya is required. Vairagya is derived from the word Viraga. Raga means desire and Viraga means desireless. If we accept Sanyasa before marriage and suddenly feel at the death moment that, “I am leaving this world without tasting Samsara”, it becomes an obstruction for Moksha and we will be born again to taste Samsara sukha. We need not necessarily be a Sanyasi to attain Moksha. But, it is essential to be satisfied in life without desires. So, it is better to undergo Samsara cycle and satisfy desires, parallely practicing Narayana smaranai from childhood and follow Sanyasa along with wife till end. In special cases, Lord will let us know, in which case, taking care of the family after one’s Sanyasa is also responsibility of Lord. For that matter, no one have the responsibility of taking care of self or others. All responsibilities lie with Him.