You contact a senator or congressman in cases of extreme urgencies (e.g. life, death, life threatening accidents) not for a visit.
The validity of the visa has nothing to do with the period of validity of the passport. Many countries their passport last less than a 10 year visa so the person must carry the old passport with the valid visa and the new passport. Many countries received a 10 year visas regardless of how long the passport will expire.
Wait for another 6 months and try to be clear that they will return in that specific date (like they have an appointment or something like that) and do not extend again their stay. The problem is that everytime does not matter how many times they are doing it they are giving the clear message that they pretend to stay longer that the maximum stay of 6 months and that is not suppose to tourism/pleasure issues and they do not suppose to want to immigrate but for immigration issues every person who apply for a tourist visa is an intending immigrant and it is in them the burden to proof the contrary...and your parents are failing since they are keep staying more than what they said at the POE.
Wait and try to find something that attach them by the time they want to return and as I said, if they get approved do not extend their stay...give it time.
Good luck,