Phones for my teenagers

[QueenofQuirkiness]

I have 3 teens, DD1 (15) and twins DD2 and DS (13), my DD3 is only 10 and will not be getting a phone until secondary school. DD1 has asked if for Christmas she could have a new phone, both she and I currently have iPhone 5S's. DD2 and DS also would like new phones, they currently have pretty cheap samsungs, which I understand isn't really the 'cool' thing anymore. What I propose to do, is to get DD1 an iPhone SE for Christmas, and also a new phone for myself, and then give DD2 and DS our old phones. DD2 and DS will have another big Christmas present in addition to the phone.
Does this sound like a fair plan, I know they are very lucky children but they work hard at school and are generally well behaved so I feel that they deserve it.

Depends what your old phones are?

how will you make it seem fair to your DD3?

(depending on colour & other specs) new iphone SE = £300ish+, do you feel obliged to give equal value gifts to your DD2-3 & DS, or do you have an established system where you usually spend more on older children?

Will all your children think it's a fair plan?

Does your plan include some kind of protective cover to fit each phone, will you flog the Samsungs to subsidise the other purchases, can your DD1 really look after an SE safely?

How big is the extra present for each of DD2 & DS?

ps: have you worked out good contracts/payment plans for each device?