Complex sentence: The Carter House Inn was originally built as a private San Francisco Home in 1884 by the famous Newsom Brothers architects, who built the Carson Mansion at the same time in Eureka.
Split into simpler sentences: The Carter House Inn was originally constructed as a (San Francisco) home in 1884 by the "builder architects" Newsom and Newsom. These famous 19th Century Victorian architectural experts also built the Carson Mansion at virtually the same time in Eureka.