Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 8 · Marriage
विवाहः
पुत्रोद्वाहात्परं पुत्रीविवाहो न ऋतुत्रये ।न तयोर्व्रतमुद्वाहान्मंगले नान्यमंगलम् ॥ ५१५ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 515.
After a son's wedding, a daughter's wedding is not held within three seasons. The thread rite of the two is not held after a wedding. In a good rite, no other good rite is held.
Simple meaning: After a son's wedding, wait three seasons for a daughter's. Do not hold one good rite inside another.
विवाहश्चैकजन्यानां षण्मासाभ्यंतरे यदि ।
Two weddings of siblings within six months may bring one woman the loss of her husband within three years.
प्रत्युद्वाहो नैव कार्यो नैकस्मै दुहितृद्वयम् ।
Do not do an exchange wedding. Do not give two daughters to one man.
नैवं कदाचिदुद्वाहो नैकदा मुंडनद्वयम् ।
Some weddings and rites must not be done twice together. Birth at certain times may risk a parent's life.