Welcome to Aquariumadvice fishand jeeps
While both fish would probably do ok in a tank together, a 55g is just too small for such big guys. The Tire Track eel gets about 2 and a half feet long, the Fire eel closer to 3 and a half feet. Way too big for a 55g. I'd suggest a 75g minimum.
As for it being an old house, you'll need to find out where the floor braces are and find out how much weight they are rated for. Then determine the weight of your tank with water, gravel and fish to see if the floor can take it.
Forget the UGF
as sweets said. Not only because they are messy, but Fire eels like to burrow.
I suggest you start off by doing some research on the fish you want. You'll need to make some decisions on tanks and fish first before considering filters if you want happy healthy fishies
aka Cycling Guru and the Ich Slayer
*glares at Terry and QTOFFER*
Card carrying member of FTAS & GCAS.