Do you think that I should date my exes brother?
Well, it depends. Do you think that your ex will care?
It's none of his business, I'll do what I want to do.
While I do agree you're free to do as you wish, I imagine it'll still be very awkward. I also think your ex's brother is a bit disloyal to take you up on that offer.
I think it will be fine, and it feels good to be wanted.
That seems like a fair and reasonable take, your ex shouldn't dictate who you can or can't be with.