Questions about example sentences with, and the definition and usage of "Tg"

A: In what context is it used in?

A: To me the second sentence would sound better if it read "Thank you. for inviting my son to her bday party, he'll be able to attend"
Or
"I wanted to let you know he will be able to attend"

it just sounds a little awkward to me saying "and he'll be able to join the party" but what you wrote makes complete sense. This is just my opinion.

I hope this helps!