Welcome to the community!
As far as I am aware, those add a line offers or other similar loyalty promotions are specific to your phone number. Other people would not necessarily be able to avail of those same offers. While you could certainly add those lines to your account for your daughter and her friend, those lines would likely need to remain on your account in order to avail of the offer. A subsequent transfer of responsibility (TOR) to your daughter and friend, respectively, would likely require them to change the plan to an in-market plan. In addition, if the offer involves financing a new phone, it appears as though there might not be possible to TOR a financed device (see here).
Hope this helps 😀