Advice needed re bungalow with separate garage to be converted to living space

Well people of knowledge.
We live in Co.Cork.
Our son lives in Co.Meath. He bought a bungalow around 7 years or so ago with a very decent size garage. He and his wife want us to move up to them permanently as we are now in our elderly years and it is a long haul for visits.
The plan would be a garage conversion. it is separate from his house but is joined by a block arch for access between both. It has one entrance to the house and would remain this way.
I would be hoping to raise the height to give up sleeping accommodation upstairs.
Downstairs would have more than adequate room for a living room, block wall dividing to Kitchen diner, and maybe go back a couple of meters to put a bathroom.
As I said the garage is pretty big as it is. I think 10 X 7 meter.
It is a well built block garage with cladding roof ( roof would be replaced obviously with either double insulated cladding or tiles.)
Anyone think there may be planning issues?
House is actually out in the sticks so to speak.
4 houses next to each other and he has spoken to them all, none would have any objections.
Also, Would this fall into the category for this "up to 70k" grants?

Thanks

From a practical perspective, if you are pushing on a bit, is stairs a good idea?. At least do them in such a way that a stair lift can be installed.

I am aware of people who have done this in the past (not in Meath) and the main proviso's were that the garage or granny flat needed to be connected to the house and it was returned to it's original use once no longer needed. In effect the council trying to ensure it could not be sold as a seperate stand alone dwelling in the future.

As above, planning shouldn't be a problem though they will insist on the two buildings being properly integrated into one and apply a stipulation that the conversion be brought into the main house once your use is no longer required. They will also likely prohibit the letting of the converted unit.

One thing you will need to validate in advance is the works and costs that will be required to upgrade the garage structure to comply with building regs as they stand today. For example, it's unlikely that the walls have a cavity and so will require insulation, and what if any insulation is under the floor?