Think there may have been another son John, the name Snell does not seem to be that common in area.
MAY, JOHN mmn SNELL
GRO Reference: 1865 S Quarter in BIRMINGHAM Volume 06D Page 109
Death - MAY'S, JOHN 0
GRO Reference: 1865 S Quarter in BIRMINGHAM Volume 06D Page 69
Maybe some of the other children birth/death certs may help trace or give more info?
Cas