Mormons and Jehovah’s Witnesses both believe in the divinity and gospel of Jesus Christ, which would, strictly, make them Christians. Since their religion isn’t based on Catholicism, that also strictly makes them Protestants.
The part other Protestants disagree with, that separates them from other Protestant denominations (such as Baptists, Lutherans, and Methodists), is that both of these sects have holy texts that are separate and distinct from the Holy Bible.
The Church of Jesus Christ of Latter-Day Saints has the Book of Mormon, which was first published by convicted fraudster and conman Joseph Smith in 1830. It was made up off the top of his head and dictated to someone who could write (Smith was illiterate), and then made up all over again (differently) when the translator’s wife destroyed the first copy. This book presumes to tell the “history” of the Christian religion in North America from 2200 BC to 440 AD. Seriously.
Their version of the afterlife is significantly different as well – Mormons have true believers inheriting their own planets to rule. Basically if you’ve ever watched the reboot of Battlestar Galactica, that’s a decent primer on Mormon beliefs.
The Jehovah’s Witnesses use the same books of the Bible as other Christians, but they have their own translation: The New World Translation. This translation doesn’t jive particularly well with any other commonly used translation of the Bible. This goes for things like the word “happy” being used instead of “blessed” in the Beatitudes – which while isn’t a great change does make some of the lines a bit weird. (“Happy are they that mourn..” I think not, actually.) And bits about the divinity of Jesus have been changed. They don’t believe in the Holy Trinity, and place Jesus a bit under God inthe holy hierarchy.
Witnesses don’t believe in Hell, they believe the end times started in 1914, and on Judgement Day exactly 144,000 peoples’ spirits will be resurrected to live on Earth 2.0 afterward (so try to be one of his favourites).