It isn’t possible to give an accurate figure.
There is no official register of home-educated children in NI – and there’s no legal requirement to inform anyone that you are home-educating.
In the United Kingdom, it is estimated that approximately 1% of “school-aged” children are educated at home; the proportion is probably lower (but growing) in Northern Ireland.
On a less numerical level…
There are enough!
Enough to make a vibrant community of families- you will find there are groups to meet with, outings to join, friends to make and other parents ready to volunteer their experience and support.