How to write a greeting when a sister-in-law gives birth to a son?

Write sincerely. The birth of a son by a younger brother and sister is a happy event in the family. As a relative, I should feel happy from the bottom of my heart. I should write sincere greetings, such as: I come to congratulate you on giving birth to a baby. I hope the newborn baby will bring you countless happiness, wish the baby good health and thrive, and wish you a sweet and happy new mother.