just a thought.. being in a somewhat similar situation.. I am also getting married here in a few months.. going from living with mom and dad and plenty of room for my tanks to likely an apartment. I've been "weeding out" my fish abit and keeping the ones I am truely attached too and like the most. But the wait has been alot easier and less stressful, because my fiance and I have had conversations about the tanks we will have when we settle down. as you pointed out the 55 is a grow-out tank.. so your full stock list is over for the 55.. you may want to give up a few fish, keeping your favorites. sounds abit silly.. but for me it's helped lessen my stress. and that seems to be the majority of what I'm reading.
as for your dad.. I'm not allowed anything more 'n a 40 gallon in my room. But my basement is fine for any size else I can fit down there. even if your dad okays keeping another 55 upstairs.. I'de set it up downstairs. set-up a "me place" .. You may be surprized but you may end up enjoying it more 'n having the fish in your room. letting your family know when you are down there it is "me time".
Thats simply how i'de look at it if i was in your situation.