I don't know if Ben or Danny write this, but it's really awesome and emotional song. It's something like apology to their family, friends, and maybe girlfriends.
"It was you that told me I could do this,
You put the music in my heart,
And how you sang with the band in Memphis,
It's hard just to be strong,
Not knowing if I've done you proud,
I like to imagine you smile when you hear my songs" It's for his grandparents. We can hear that they are probably dead now, and he hopes that they are proud of him. He really loved them, and still love them.
"A letter home and I know we don't speak much.
And we both know I'm not keen to but I think there's things I've left unsaid.
I'm okay don't worry.
I wish I'd been a better kid.
I'm trying to slow down.
I'm sorry for letting you down" It's for his parents. When he ran away to America, he didn't said goodbye to them, He wish to be better kid (Maybe he was loser or he was really "bad boy")
"You know it's just rock and roll,
I know you're by my side through it all,
My terror twin and I,
Let's take over the world" It's for Danny/Ben. They were like twins to each other, like brothers.