A weird set up to say the least. I can apply for Irish citizenship through four Irish Grandparents but can't pass it down to my two sons. I can however pass it on to any kids they might have. To qualify your Grandparents have to be Irish citizens when you're born, an odd rule..
I've ordered the long copies of my Grandmother's birth and marriage certificates and I already have her original death certificate, I could apply in a couple of weeks by the look of it. The fee is steep at around £300 but I'm seriously giving this consideration. My son is about to start work in Germany and his Norwegian girlfriend is going to live with him, with the uncertainty of Brexit this feels instinctively the right thing to do, even if it doesn't help my son directly, maybe things could change in the future.