Incidentally, Heol Hen = Street, Old, ie Old Street.
In the 1861 Census, there are two JE entries in Llanelli; but neither fit readily to your information, suggesting that the family had left prior to that Census - which seems to make sense for that long sea voyage.
Even less certainty in the 1841 Census, only Llanelli possibility-
1841 census transcription details for:Drinen Bicca, Llanelly, Berwick Print Close National Archive Reference: RG number: HO107 Piece: 1379 Book/Folio: 2/4 Page: 1 Reg. District: Llanelly Sub District: Longhor Parish: Llanelly Enum. District: Ecclesiastical District: City/Municipal Borough: Address: Drinen Bicca, Llanelly, Berwick County: Carmarthenshire Name Relation Sex Age Birth Year OccupationWhere Born EVANS, MaryF 55 1786Carmarthenshire EVANS, WilliamM 20 1821Carmarthenshire EVANS, JohnM 14 1827Carmarthenshire
I have also tried to find their Marriage on the same site - but only one possibility-
Civil Registration event: Marriage Print Close Name: SAMUEL,Margaret Registration district: Swansea County: Glamorganshire Year of registration: 1848 Quarter of registration: Oct-Nov-Dec Spouse's last name: Not available before 1912 Volume no: 26 Page no: 715 MarriageFinder:Margaret Samuel married one of the following people:
EVANS, Evan JENKINS, Benjamin JENKINS, Daniel RICHARDS, John EVANS, Hannah THOMAS, Mary WILLIAMS, Charlotte