When the Church published the Creed, did they, at the time, mean to include the saints in Heaven as well as those on earth, with the phrase, “Communion Of Saints?”
Absolutely. The dead martyrs and such were venerated right from the earliest days. If you read the account of St Polycarp’s martyrdom written at the time - the 150s AD - it speaks of his bones being gathered up and venerated after his death.
And there are prayers to the deceased written on the walls of the catacombs dating from before the Nicene Creed was written at least. So certainly it was believed that the dead could intercede for and pray with the living and formed part of the one ‘body of Christ’.
Yes. After all, Christ communed with saints at his transfiguration, per Matthew 17:
1: And after six days Jesus taketh Peter, James, and John his brother, and bringeth them up into an high mountain apart,
2: And was transfigured before them: and his face did shine as the sun, and his raiment was white as the light.
3: And, behold, there appeared unto them Moses and Elias talking with him.
4: Then answered Peter, and said unto Jesus, Lord, it is good for us to be here: if thou wilt, let us make here three tabernacles; one for thee, and one for Moses, and one for Elias.
5: While he yet spake, behold, a bright cloud overshadowed them: and behold a voice out of the cloud, which said, This is my beloved Son, in whom I am well pleased; hear ye him.
6: And when the disciples heard it, they fell on their face, and were sore afraid.
7: And Jesus came and touched them, and said, Arise, and be not afraid.
8: And when they had lifted up their eyes, they saw no man, save Jesus only.
Those who argue against the communion of saints need to explain where Moses and Elias came from and why Christ was talking with them in light of their alternate understanding.