SapphireStrange re "sorry but 'a little awkward' is not a reason to let someone in when they come round uninvited, IMO."
Most people would fine it very, very hard (unless the grand parent was abusive) to turn away their child's grandparent at the door, especially when the child has seen the grandparent.
OP I think you need to get on the offensive not the defensive. Take the calls, go broken record. You can always end a call with the words.
"I am sorry you feel like that but it does not change my mind.
Please do not come round today/tonight, I am very busy and will not be able to let you in for a chat.
I am putting the phone down now and will speak to you soon."
Then after the warning, if he does come round, explain to dd first. it's grand dad but he just wants a quick word, he cannot stop, and we are busy, doing XYZ..."
Go to door and say through door, sorry we are busy now or if he has a mobile phone it and say, I can't come to the door right now.
If you feel strong enough make sure dd is elsewhere in another room and go to door and say to FIL "This is not acceptable I was very clear we are not available today. Please call tonight to speak to dh and I."
Then you and dh need to make it clear that FIL coming round and getting upset is not acceptable and will not resolve this situation, it will only prolong it to everyone's detriment, including dd (if it is true she is being upset by this situation) or you who is being VERY upset by this situation.