He is.

[He smiles fondly.] He's...good for me. It helps having him around.

But he also sees Choco as a daughter, and I really can't see her as one, she's my sister, and I'm pretty sure Donnie would not approve of a change in relationship just because I'm getting together with Mac.

So I don't think you're getting any siblings out of that, you'll have to adopt them as siblings on your own if you want them.