I think it's a pretty interesting premise!
I would like to be able to offer, but I already have so many character concepts that it would probably be pretty irresponsible of me.
It may be interesting for people who would be willing to play your character's brother to see some of Aidan first? Maybe some test, non-canon RP with your character to have an idea what he's like and such? I find that the better I know a character, the more comfortable I am coming up with a full concept for a relative.
I also think three things would be relevant to know:
One is to know if you are open to him not actually having murdered their father. This would encompass a great deal more possible concepts than if he did do it.
The second is to know what their father is like (this would greatly affect whether or not a murder was justified, for instance). If he might've been abusive, or dealing in something shady, or terminally ill, or basically anything that could make killing him sound less... criminal.
The third would be less plot relevant: a picture of Aidan. Sure, you said the player can decide what his brother looks like, but brothers will rarely look completely different (unless they're half brothers, or adoptive brothers). So if they are full blooded brothers, it's more likely they'll share traits, like skin color, or eye color, or hair color, or all of them. Height may also be similar.
Do take my advice with a grain of salt, though. I like planning and I like making sure everyone is on the same page when it comes to playing relatives and joint plots. Characters don't need to know the same things, but OOC I think the players should have the same amount of information about the family background, to avoid unpleasant surprises (e.g. the other player building their concept around the idea that the father was a terrible man and nothing like you, ooc, imagined.)
I would like to be able to offer, but I already have so many character concepts that it would probably be pretty irresponsible of me.
It may be interesting for people who would be willing to play your character's brother to see some of Aidan first? Maybe some test, non-canon RP with your character to have an idea what he's like and such? I find that the better I know a character, the more comfortable I am coming up with a full concept for a relative.
I also think three things would be relevant to know:
One is to know if you are open to him not actually having murdered their father. This would encompass a great deal more possible concepts than if he did do it.
The second is to know what their father is like (this would greatly affect whether or not a murder was justified, for instance). If he might've been abusive, or dealing in something shady, or terminally ill, or basically anything that could make killing him sound less... criminal.
The third would be less plot relevant: a picture of Aidan. Sure, you said the player can decide what his brother looks like, but brothers will rarely look completely different (unless they're half brothers, or adoptive brothers). So if they are full blooded brothers, it's more likely they'll share traits, like skin color, or eye color, or hair color, or all of them. Height may also be similar.
Do take my advice with a grain of salt, though. I like planning and I like making sure everyone is on the same page when it comes to playing relatives and joint plots. Characters don't need to know the same things, but OOC I think the players should have the same amount of information about the family background, to avoid unpleasant surprises (e.g. the other player building their concept around the idea that the father was a terrible man and nothing like you, ooc, imagined.)