The givaway here are the collars of the boys at the front,the one on the left being introduced around 1909 & on the right the chap has a soft collar with pin which I haven't seen prior to WW1 so may even be a bit later.By 1920 these boots were being replaced by shoes particularly amongst younger men,owing partly to the fact garters to hold up socks were now popular.I would say you are looking for 3 brothers born around 1885-95.
jim