We just had DDs traditional church wedding in June. Both FOB and FOG wore tuxes. However, I do think it could be up for discussion if money is an issue. Personally, I think if both fathers were wearing dark suits it would be just as appropriate and, really, more practical. I have been to weddings where even the groomsmen wore their own dark suits. I would suggest a very frank discussion with your son and his his bride-to-be. While I love traditional weddings...there sure is alot of money spent for just a few hours!