Both feature the daily lives of mystical beings. Saint Oniisan focuses on Jesus and Buddha, while Hozuki is about the staff of Japanese hell, but they have a similar sense of humor regarding things that should seem completely ordinary. Both bring in other famous mythological figures and are a lot of fun to read.
When I read Arakawa under the bridge the surreal humour striked me as quite pecular.
I felt like I got a similar feel from another manga before. I checked the author/artist and ... yep... It's the one from Saint Young Men! Both have similar humour. In good kind of way.
The similarity in these two series arises from their exploration of holy beings. In the case of Kamisama Kazoku, we are introduced to a family of god and his angels. In the case of Saint Young Men, we follow Jesus and Buddha in contemporary Japan.