can my 15-year-old brother leave the UK to go back to his home country without being accompanied by the stated accompanied person in his UK visa?

my younger brother who is 15 is going to visit me in the UK with my dad as the adult accompanying him. But my dad is only going for two weeks and my brother will go back 2 weeks after him. They are coming from Indonesia.

My question is, will they let him board the plane to go back to Indonesia? Since there will be no immigration exiting the UK, I presume that there won’t be any problem?

I will be sending him off to the airport until he gets on the plane. Please advise. Thanks

Can I travel to the UK unaccompanied on an accompanied visa, if I have my mother’s passport and letter giving permission? [duplicate]

This question already has an answer here:

  • Transiting from the US through the UK on a Child Visitor visa 1 answer

My visa says ‘Only valid if accom by’ my mother’s name and passport number. I am not in the same country as my mother so I cannot travel with her but she can send me her passport and written letter, would I be granted access to the UK?