If the property was built in 1961 then (depending on the Local Authority) there's probably no planning documentation for it- planning permission was introduced in 1963 and Building Regulations came into being in 1989 IIRC. Some Local Authorities had by-laws requiring approval before construction but these were the minority I believe.
- Any extensions post-1963 would require permission if not exempt.
I'm making an educated guess that the land was obtained (by your grandparents or whoever they bought/inherited it from) through a Land Commission purchase. (If it wasn't that'd suggest a direct purchase from whatever aristocrat had it as part of their estate which in most parts of the country was rare, and even rarer outside of the towns). In that case there's a folio in the Land Registry.
So basically go onto the Land Direct website, do a map search to identify the folio, get a copy of the folio (costs €5 and will arrive in your email as a PDF in about 5 seconds).
- Part 2 will show the ownership
- Part 3 will show any burdens, including mortgages
I'd be very surprised if there was any clawback from a house built in 1961. There may be a clause saying that any transfer/mortgage is subject to the consent of whatever local authority but I'm pretty sure this would be null at this stage (I think the law changed since the last time I did conveyancing of an ex-council property) and even if it's not the consent will be given automatically in the circumstances.
If there are extensions you may need to get an opinion on compliance/exemption with planning permission/building regulations depending on when it was built. In the worst case scenario where you have to apply for retention before the sale that'll still be faster and easier than the actual probate process itself.
If there's no mortgage and no extensions then it's entirely possible that there are no title deeds other than the land registry folio.