I like big butts and I cannot lie, my other brother also likes big butts and cannot tell the truth, how will you escape our dungeon
A thought occurs. If your other brother can’t tell the truth, how do we know that he likes big butts in the first place?
Because he says he doesn’t like big butts. The truth telling brother knows this is a lie and can extrapolate that the liar also enjoys big butts. The real question is whether other not the one who claims to be unable to lie is truly the one who cannot lie or if that was an addition to make the statement a lie because he’s the real liar.
Clearly the solution is to ask either of them what butt the other would prefer