Actually, I do not have a problem with this. He is calling on them to witness to them regarding the sacrament. Do you support the sinner who has determined that their sin is in grave danger and answers the call to forgiveness? I sure hope to hell you do!!!
Full context requoted:
Francis told the priests that for “every person and every situation you are called to be fellow travelers to witness and support.”
He urged them to “support” all couples who have determined by themselves that their marriage is invalid and want it officially declared as such.
“When you offer this witness, may your care be also to support all those who have realized the fact that their union is not a true sacramental marriage and want to come out of this situation. In this delicate and necessary work, proceed in such a way that your faithful recognize you not so much as experts of bureaucratic acts or juridical norms, but as brothers who put themselves in an attitude of listening and of understanding,” he said.
There is no sacrament or sacramental grace in cohabitation, i.e. fortification.