I have made an attempt at Thomas Edwards' family but have not found brothers for Frances as you described.I could,of course,be entirely wrong,but for what it's worth this is what I came up with:-
Thomas Edwards(1773-1841).I believe he was married twice,first to Anne Williams(1780-1816).
I have not found their respective baptisms or marriage,but their children are Frances(Ffestiniog,1805),Elizabeth(Carnarvon,1809),Samuel(Llanllyfni,1813-1814).
With the records being non-conformist,these dates are close to the start of some records and there could be scope for others not recorded(or missed by me?).some databases have interesting variants on names(Family Search has Phanny Edwards,Thomas Edwarts,Jane Griphith )- see IGI batch number C 103491 at
http://freepages.genealogy.rootsweb.ancestry.com/~hughwallis/IGIBatchNumbers/CountyCaernarvon.htm#LI believe his second marriage was to Jane Griffith(1786-1868) in 1817 in Llanfihangel y Pennant.Marriage details at NLW marriage bonds and allegations.Their children are(with Talrwst(sic) references for first and last)-Mary(1819),Edward(1821),Jane(1823),Catherine(1825) and Griffith Thomas(1829-is this the "brother" Thomas?).
Some of the family can be seen in the 1841 census at Bryn Nenan(?),LLandwrog ref.HO 107 1397 2/39 7.
I also think that Catherine(1825,above),may be with Frances at the Talysarn shop(HO 107 1397 2/93 2).
The burial entry for Thomas Edwards is at Rhos Nenan(?),with a side note - "late of Talrwst"
This property appears to be in the possession of an Owen Griffith,son of William Griffith,weaver(1832 will at NLW).His second wife is at Bryn En(g)an until her death in 1868.
Regards
Roger