They might be triplets - or simply a "mass" baptism , was father John ill ? were they ill ?

If there is no further mention of them perhaps they are lodging with a friend/family by 1851, or if old enough in service. They may be transcribed/recorded under the family surname .

many possibilities.

and then an Amelia "turns up" in Wales to marry, and she was born 1845 Lydbrook !!!