Looking at the births on FreeBMD, all 3 have a mother's maiden name of Shuttleworth.
The only marriages I can see for a Shuttleworth to a Shuttleworth are:
1916 in Toxteth Park (Annie & William)
1916 in Bolton (Agnes and Albert)
It may be that their mother wasn't married?
So, probably best to buy a birth certificate, I feel, as parents names will be on that.