 There were actually 3 Chamberlain brothers at Gettysburg although  only two are in the film. Brother John Chamberlain was a Doctor who  had come down to visit his brothers Joshua and Thomas. When Lee  invaded Pennsylvania John stayed with the 20th Maine to help. He  treated the wounded of the 20th Maine on Little Round Top as well as  helping afterwards at various field hospitals. The line in the film  "Split up, another close one like that and it could be a bad day for  mother" was actually said by J L Chamberlain to his brothers John  and Tom. A shell had exploded in the trees over their heads as they  climbed up Little Round Top together giving them a rather close  call.