Did Jane and Thomas marry in Ireland, or possibly have any children that might have been baptised here ?
The surname Borthistle (Borthisell) shows up in the area in the 1820s, e.g. in Kilpipie civil parish which is split between counties Wicklow and Wexford.
If so a search for details of these might be a good place to start to narrow down which part of County Wexford these events took place in - i.e. which town or parish.Currently there is only very patchy coverage of Church of Ireland and other ‘Protestant’ registers for County Wexford on websites so online research is very limited - combined with that is the issue of lost records, so knowing the parish or at least a narrow area where 'your' Donovan, Sly or Borthistle families lived is important.
Pay-website RootsIreland has some partial transcripts for two parishes in the county and there are no major collections of Church of Ireland or other ‘Protestant’ vital records on FindMyPast or Ancestry. FindMyPast does have some secondary record collections - e.g. Marriage License Bond Indexes, extracts from old registers etc.
The Representative Church Body Library (South County Dublin) hold most of the historic Church of Ireland records and they are currently running The Anglican Record Project - this is a major project to digitize the old registers so will take some time, but already includes two parishes covering parts of county Wexford… worth keeping an eye on progress of this to see if Sly records show up…
Edit - previous related topic for reference : Borthistle family from Ferns,townland of Effernogue
note the Borthistle / Donovan marriage mentioned in this topic was in the Diocese of Ossory, which covers parishes in Counties Kilkenny and Laois (formerly Queen's county) , so to the west of county Wexford. Marriages generally took place in the bride's parish, so might suggest that this Donovan family originated, or at least lived, in Kilkenny or Laois..
