祖宗 is read as そそう (sosou) and means ancestors.
そそう
sosou
こうそこうそう
ancestors of the Imperial Family
しゅうそ
sect founder
かいしゅう
religious conversion
ぜんしゅう
Zen (Buddhism)
しゅう
tenets (of a religious sect)
むね
instructions
じょうどしんしゅう
Jōdo Shinshū (offshoot of the Jōdo sect)
てんだいしゅう
Tendai sect (of Buddhism)
じょうどしゅう
Pure Land sect (of Buddhism)
しんぎしんごんしゅう
Shingi Shingon ("New Shingon" school of Buddhism)
ほうそうしゅう
Hosso sect of Buddhism (Japanese equivalent of the Chinese Faxiang sect)
いっこうしゅう
Ikkō sect (of Buddhism)