Your texts have been perfect!!
However angry you were, it was spot on & you remained calm, cool & collected.
To be honest, I'd not reply
It'll just keep going backwards & forwards. Also, if one of them does cause any upset at the party, it'll ruin Ryan's day and the day is about him
It's a real shame, but he's made the decision now
not to be there and there's not a lot you can do about it
If you keep playing middleman with them, they'll do this for every event where they're both invited, and it's not your place (and why should it be?) to keep them both happy.
Must be so frustrating for you & Nat.
I reckon he'll either have a think about his decision before the party and decide that for the sake of Ryan (and to save himself a lot of guilt) he'll just go and not cause an atmosphere, or he'll realise AFTER the party that he was very silly and will feel ashamed that he put his own selfishness before the happiness of his first Grandson's special day.
You've done all you can now, the ball is in his court. I don't know what else to suggest
xx