As for mortal sin versus venial sin, any sin can be mortal if one acts from malice of God’s will.
Yet, it’s difficult to list mortal sins versus venials sins, because there are objective and subjective elements involved. For a sin to be mortal, three things must be present: 1) grave matter, 2) full advertence of the mind, 3) perfect constent of the will.
“There is sin that is mortal… there is sin that is not mortal.” (1 John 5:16-17, NRSV)
“When the will sets itself upon something that is of its nature incompatible with the charity that orients man toward his ultimate end, then the sin is mortal by its very object . . . whether it contradicts the love of God, such as blasphemy or perjury, or the love of neighbor, such as homicide or adultery. . . . But when the sinner’s will is set upon something that of its nature involves a disorder, but is not opposed to the love of God and neighbor, such as thoughtless chatter or immoderate laughter and the like, such sins are venial” (Catechism of the Catholic Church, 1856, St. Thomas Aquinas, STh I-II,88,2)
Rejecting sententia certa (certain teachings) of the Catholic Church is not heresy or schism, but is sinful disobedience, and can be mortal depending upon voluntary malice for the divine will. Canon law binds all Catholics, and directs us to give our religious submission of mind and will to all Catholic doctrines taught by the authentic magisterium. (canon 750, Lumen Gentium 25) It’s a sin against charity to not submit to the lawful pastors in matters within their scope of authority, an authority given to them by God. It is just as sinful to disobey civil laws established by lawful authority, also given by God. All such sinful defiance of lawful authority is contary to Scripture…
Heb 13:17 “Obey your prelates, and be subject to them. For they watch as being to render an account of your souls; that they may do this with joy, and not with grief. For this is not expedient for you.”
For more, see Ad tuendam fidem - John Paul II and the - Professio fideiDoctrinal****Commentary by Joseph Cardinal Ratzinger.