This time I'd like some resources to convince someone heretics can possibly administer sacraments that confer sanctifying grace. I have been talking to someone who was sedevacantist and then went Eastern Orthodox and converted back to the faith but he is arguing that heretics can't confer sanctifying grace to an infant via baptism or an Orthodox priest communing an infant. I showed him Exultate Deo from Florence but that didn't convince him. He also said he doesn't believe age of reason.

Pope Eugene IV, Council of Florence, “Exultate Deo,” 1439: “In case of necessity, however, not only a priest or a deacon, but even a layman or woman, yes even a pagan and a heretic can baptize, so long as he preserves the form of the Church and has the intention of doing what the Church does.” (Denz. 696)