Complex sentence: The Ymer family ran the boarding house successfully during the 50s, 60s, 70s and 80s, earlier, for accommodation for new immigrates that arrived to Melbourne: but later the accommodation business declined, as did the quality of the building.
Split into simpler sentences: The Ymer family ran the boarding house successfully during the 50s, 60s, 70s and 80s. In the later years the accommodation business declined, as did the quality of the building.