The presence of the doves with Saint Joseph is a reference to Luke's Gospel, 2:22-24:
And when the days for their purification were fulfilled, according to the Law of Moses, they brought him to Jerusalem to present him to the Lord, as it is written in the Law of the Lord: Every first-born son shall be dedicated to the Lord, and to offer as a sacrifice, according to what is said in the Law of the Lord, a pair of turtledoves or two young doves.