A method of installing a wellbore junction assembly in a well can include inserting a tubular string into a deflector, and opening a flow control device in response to the inserting. A well system can include a deflector positioned at an intersection between at least three wellbore sections, and a tubular string connector having at least two tubular strings connected to an end thereof, one tubular string being received in the deflector and engaged with a flow control device positioned in a wellbore section, and another tubular string being received in another wellbore section. Another method of installing a wellbore junction assembly in a well can include inserting a tubular string into a deflector positioned at a wellbore intersection, then sealingly engaging the tubular string, and then opening a flow control device in response to the inserting.