When I was in college, I had four really good friends and we were all in the same club.
ご質問ありがとうございます。
"When I was in college,"＝「大学にいたとき」
"I had four really good friends"＝「4人、とても仲の良い友達がいた」
"and we were all in the same club."＝「そしてみんな同じクラブに入っていた。」
（又は、*and we all belonged to the same club.*=「そして、みんな同じクラブの属していた」とも言えます。）
ご参考までに。
When I was in university, I had four really close friends who were in the same club I was in.
この場合、次のような言い方ができますよ。
ーWhen I was in university, I had four really close friends who were in the same club I was in.
「大学の時、私と同じクラブに入っていた仲の良い友達が４人いた」
to have four really close friends で「仲の良い友達が４人いる」
friends who were in the same club I was in
で「私と同じクラブに入っている友達」
ご参考まで！
アメリカ合衆国 
カナダ 
