Complex sentence: All the Butlins hotels of the 1950s--1990s were sold in 1998 but the majority are still open today under different ownership, the art deco style Ocean hotel at Saltdean has been redeveloped into apartments and the hotels at Cliftonville have both been demolished.
Split into simpler sentences: All the Butlins hotels of the 1950s to 1990s were sold in 1998, but most are still open today under different ownership. The art deco style Ocean Hotel at Saltdean has been redeveloped into apartments, and the hotels at Cliftonville have both been demolished.