The 1851 Census suggests that Hezekiah was the son of Miles. This is the entry:

1968 0045 043 Duntisbourne Abbots FREEMAN Miles HD M 42 Ag.Lab GLS Duntisbourne Abbots
1968 0045 043 Duntisbourne Abbots FREEMAN Elizabeth WI M 42 - GLS Sapperton
1968 0045 043 Duntisbourne Abbots FREEMAN Hezikiah SO U 16 Cowman GLS Duntisbourne Abbots
1968 0045 043 Duntisbourne Abbots FREEMAN John SO - 13 Shepherd Boy GLS Duntisbourne Abbots
1968 0045 043 Duntisbourne Abbots FREEMAN Louisa DA - 5 - GLS Duntisbourne Abbots

This family next door:

1968 0045 044 Duntisbourne Abbots FREEMAN John HD M 45 Ag.Lab GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots FREEMAN Maria WI M 42 - GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots FREEMAN William SO U 17 Ag.Lab , Carter GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots FREEMAN Henry SO - 14 Ploughboy GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots FREEMAN Edward SO - 11 Ploughboy GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots FREEMAN Caroline DA - 9 Scholar GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots FREEMAN Robert SO - 7 Scholar GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots FREEMAN Mary Ann DA - 1 - GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots FREEMAN Alfred SO - 2M - GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots KILMISTER Jane LG U 62? Ag.Lab GLS Duntisbourne Abbots
1968 0045 044 Duntisbourne Abbots KILMISTER David LG U 29 Ag.Lab GLS Duntisbourne Abbots

The ages of John and Miles are not the same so not twins either?

The IGI gives this baptism for Miles:
17 April 1808 at Duntisbourne Abbots. Parents John FREEMAN and Mary

John FREEMAN does not appear to have been baptised with Miles further suggesting they were not twins.

Mike