… the Church can allow the priest to give them communion so they have the grace and medicine to increase in truth.
The couple in question have to examine their conscience — which is to be conformed to the teachings of the Church — and to repent of their mortal sins (such as they may be) as well as go to Confession before they can receive the Most Holy Sacrament of the Altar.
If they receive Christ in a state of mortal sin, they receive absolutely no grace and absolutely no medicine.
Instead, they commit a sacrilege, which is a further mortal sin.
Anyone who says any differently is spreading falsehoods which are incredibly dangerous because they can encourage souls to willfully embrace hell.
As for us, we don’t judge whether or not any individual — other than ourselves — subjectively is in a state of mortal sin. That requires information we don’t have access to. It is, amongst other things, the sin of usurpation: only God has the ability to look into hearts. Moreover, charity demands that we bend over backwards to avoid making rash judgments, and if we fail in this regard, we are endangering our own souls.
However, on an object level, we are perfectly able to look at behaviors and determine whether or not they contradict God’s moral law as revealed to His Church. Furthermore, especially when we have responsibility over another, it is our duty to encourage a person who is objectively sinning to repent and to do penance. Again, charity demands that we do such a thing, because it greatly increases their likelihood of avoiding hell by repenting of their sin. To simply tell such a person, “well, I can’t judge you” is, for cowardly reasons and for human respect, to avoid our obligations to our neighbor.
We will answer to God for both of these sorts of sins.