Hashi and Second I thought lost two brothers. Kawarama and Itama...They all have the ama endings..which I am not sure if that was custom back then or now. I don't even know if AMA means anything but Hashirama, Tobirama, Kawarama and Itama.
1) It's uncertain if Kawarama was a sibling to the other 3, they never address him as brother. Only thing we know for sure is that he was a fellow Senju.
2) The Kanji in common between Hashirama and Tobirama is 間 (ma; "room, space"). Hashira and Tobira mean "pillar" and "gate", respectively. Itama is most likely a pun, considering 板間 (Itanoma; "[room with a] wooden floor") is composed by the kanji for ita and ma. Just for curiosity's sake, Kawara means "tile".