You know, even though there's no way dad & daughter could actually get married, (being as they are, you know, dad & daughter,) they COULD just fake it. They already legally have the same surname and are planning a move to a new city: just slap on a couple rings and represent themselves to everyone in the new location as man & wife. They'd have to break with most everyone who knew they were related, (except the few who might be in on it - like Elena,) but it's a plot device that has been used before, (at least with a brother & sister pair).
R.I.P. George H. W. Bush.