(Either you have a big enough house for it, or you don’t have the money for multiple residences, regardless.)
Literally: accumulate – generation – same – reside
Alternately: Multiple generations of a family living in the same house. In some cases, the phrase may be used to celebrate the good fortune of a household that has seen enough health and prosperity to allow this situation to come to pass.
Notes: This is a compound of compounds: 累世 refers to multiple (successive) generations; 同居 is “living together.”