This will be assessed on a case by case basis as each supplier can have different policies in place.
In the case of flight bookings, it's usually not possible to add an additional traveller to a booking. In most instances, you will need to make a new booking for the additional traveller, and then pay for seat selection to sit next to each other on the plane.
In the case of hotels and activities, please email support@travala.com with your Order Number and our team will check on policy availability and direct you how to proceed.