the odds are it will never happen ,number 1 brother don't like getting naked together much lest sharing a lady one been having sex with ,,maybe if they pick you up in a bar together and took you home and they did not know you ,,, I try once with twin brother and could not get it to happen in the end I had sex with both of them but not in a threesome at different time one at his place and the other brother at my place,, that might be your best hope of having with both of them and hope they don't tell the other one