Your wife needs to understand that the larger tank you have, the easier it is to keep clean! (meaning, small tanks foul REAL fast, larger tanks and their biological systems, with weekly water changes and parameter testing will maintain themselves very well!)
She also needs to understand that you could spend money on this hobby or one that takes you out of the house...LOL which would she prefer?
When you say a small house how small?
i live in a end trerrace and i have tanks all over the place, mainly in the dining room but she lives with it, after all i dont go out drinking with mates seeing as i dont have any
p. demasoni are very aggressive fish. They need the footing of a larger tank to help provide room for lots of hiding spots and room to "run" from the aggressor!
The Yellow Labs will be fine, but the Demasoni are going to need a bigger tank. Like KJ mentioned, they're really aggressive and need to be kept in large groups. Why not go with the C.Afra species instead ? Those, with the Yellow Labs will make a nice contrast of yellow and blue colours, just like the Demasoni would...