I know I am going against the tide here, but I'd make a quilt for the older child ONLY. There will be all sorts of baby gifts arriving and nothing will be for him. Not sure of his age, but if an I Spy would entertain him, he's pretty young. *We* know that everything isn't about him, but at his age, all the attention to the baby will be hard to take. Not only that, I'd buy a nice blanket for the young one and let big brother know he gets a quilt because he's bigger. He'll have something special to show when the admiring relatives show up to see the baby.
And I wouldn't be fulfilling any wish lists, either, unless I really wanted to. Aren't the onesies inexpensive to buy, compared to the time to make them? And they are outgrown so quickly.
hugs,
Charlotte