pretty basic, when they were younger he was jealous when she was born and it carried out into their younger and even older years but not in a really bad way. he picks on her now, but probably mostly out of love, especially after their younger brother was born. they don't have to be extremely close, but i had it set that they were born in dublin, ireland and their parents died in a car crash and they were sent to move to london with their aunt. he would've been old enough to be on his own since she was 15 at the time, so he could've either still been at home or on his own at that point.