If FTM states that they are cousins twice removed then the mistake, if there is one, occurred further back than on the individual page. You will have to go up your brother's wife's ascendancy tree and try and identify where the mistake occurred.
If you go to the top of your brother's wife's branch and then run a Outline Descendancy report do you get numbers like this [1] after the generation number? That usually indicates inter-marriage. You will then have to work out where the inter-marriage mistake occurred and it should be above where the inter-marriages numbers starts on the report.