You don't actually say where these Freedom Records are.
London Metropolitan Archives?
Are they on Ancestry? (I don't have a sub).
Otherwise have you tried contacting the LMA to get copies?
The will of Thomas Rowsell date of probate 15th Sept 1773 of Wimbledon, was at the PCC.
Do you have it?
It's only a very short will.
It is free at the moment on The National Archives, or you can get it on Ancestry if you have a sub.
I suspect this is the same man you have as dying 5th Sept 1773.
He doesn't mention his wife, so I presume she has already died.
He mentions sons William and John, and three daughters, two of whom are married. One is called Betty Fuller, married to a Thomas Fuller, who looks as if he must have been a relation to the Thomas's wife Sarah Fuller you mention.
But this Thomas Rowsell states he is a 'farmer' in this will, so presumably no admission to the city of London via a butcher's apprenticeship.
Have you looked for any Land Tax records for him? (These are on Ancestry).
These's an interesting item that comes up on a Google search for "Thomas Rowsell" Wimbledon.
On Ancestry someone has posted an 'obituary' for him.
The introductory snippet for a Thomas Rowsell born in 1702 says:
"Thomas Rowsell was a tenant farmer on the Duchess of Marlborough's Wimbledon estate......."
As I said, I don't have an Ancestry sub to get to the rest of it.
(This may be something you have put on there for all I know!)
There must be some records for these estates somewhere. Have you tried to track them down to see when his leases began, and if there is any other information about him?
If he had 'leases for lives', he may well have mentioned his sons.
If you think he came from Somerset, have you looked at Rowsell families there in the right time frame?
Once again. I'd look for any wills that might mention him, both at the PCC (on TNA or Ancestry), or trawl TNA for any mention of land deeds etc. Don't just look at wills for any one who may have been his father - spinster aunts and bachelor uncles were also very good at leaving bequests to their nephews and nieces.
I see TNA has some 24 'hits' for "Rowsell" Somerset, between 1600 and 1800.
The TNA site doesn't do variations of names, so you would need to try other spellings on a separate search. I've seen 'Rouswell/ Rosewell/Rosewall/Rowswell' etc.
What about the Somerset Archives?
Have you had a dig around in their catalogue?
https://swheritage.org.uk/somerset-archives/It might involve a lot of digging.