Most of the painted portraits were not dated.

John (Thomas) Agglington was born on 12th January 1764 and married Ann Catlin on  4th June 1784 at Abbey Church, St Albans. 

They had two children Mary and Thomas:

Mary was christened on 25th July 1784 at Abbey Church

Thomas was christened on 12th Feb 1786 at Abbey Church

According to the Victoria & Albert Museum the clothing is

Thomas as a young man

c.1801-05 making Mary c.20 years old  in the portrait

Thomas married Ann Pullen on 16th May 1819 at St Marlebone New Church' London, ( as Thomas AGGLETON) [Note 1]

Thomas  and Ann had eight children only two of whom are shown in miniatures: Thomas James and Ann

Thomas James  was 3 years,7 months & 18 days old when  Ann was born on 21 December 1823
this portrait was painted by Mrs Tiller of 16 New Street Dorset and died on 21 April 1827
Square on 6 November 1823

Thomas James in later life (note 2)

"Uncle George":

RGA has the original of this: John & Mary speculated that

Referred to as such by Charles Aggleton (1857-1937)

this was a also a portrait of Thomas later in life. Unlabelled

Victoria & Albert Museum put dress c.1805 [Note 3]

[Note 4]

Note 1: There is no definitive proof that the Thomas AGGLINGTON  baptised in St Albans is the same person that married Ann Pullen with the surname changed to AGGLETON. However the fact that the family "heirlooms" contain miniatures of John AGGLINGTON and Thomas AGGLETON  would help to indicate that this is a valid assumption. [MJA]
Note 2:This miniature, owned by Peter/Jane, is most likely Thomas James  in later life, especially as he suffered ill-health  and is likely to have been over-weight.[MJA]
Note 3: If the V&A have correctly identified the clothes then for Charles to have "known" Uncle George is a bit unlikely. Charles may have simply been aware of the miniature. This could be refering to a great Uncle or even a non-member of the family since the epithet was used to describe any older person. There is no suitable candidate in the Aggleton family tree. [MJA]
Note 4:The similarities between the two frock coats of "Uncle George" and the "Thomas" portrait are self-evident. Thomas died in 1842 at the age of 56 and this could have been a portrait in later life, but at this stage it must be considered as speculation [MJA]