Unfortunately it's not looking very promising in terms of locating vitals records on your Maguire/Donohoe family....
As you have probably already discovered Tomregan is a Civil parish primarily in County Cavan but also partially in County Fermanagh. The townland of Snugborough is in Tomregan civil parish and adjacent to the village of Ballyconnell, Carrowmore townland is located immediately to the west of Snugborough.
I've attached a modern map with the townland boundaries marked below for the area surrounding Ballyconnell.
Civil registration started a little after your family left, so a search of Church records would be required to establish baptisms & marriages etc. Three separate Catholic parishes covered Tomregan civil parish in the early 1800s :
Drumlane with chapels at Drumlane and Staghall
Knockninny with chapels at Knockaninny, Glassmullen, and Drumderrig
and a parish Union of Kildallan/Killdallin and Tomregan (Ballyconnell) with chapels at Ballyconnell, Ardloher and Kildallan
The last one would seem to be the most likely parish for your Maguire/Donohoe line.. as it's closest to the location you mentioned. The Ballyconnell chapel was slightly to the south west of the town and in the townland of Cullyleenan.
In an 1837 listing (Lewis) the chapels at Ballyconnell and Kildallan are noted as being thatched buildings.
Unfortunately none of these parishes has very early records - the baptisms and marriages for Kildallan and Tomregan Catholic parish only cover back to 1867, no earlier records are documented for this parish, even though the parish and chapels are noted as existing back to the early 1830s at least.
The other two parishes are a little better, those for Knockninny go back to 1855, and those for Drumlane back to about 1836.
I checked for Catholic baptisms of any of the children in North Cavan/South Fermanagh area in the available records, the only matches by parents names I found were in County Longford and much too late - 1880s.
I've also attached a wider view of the area showing the locations of the Catholic Chapels as they were in the 1830s.The slightly darker blue boundary is the County border between Cavan and Fermanagh - the other part of Tomregan civil parish is to the north east of this.