In one story, I have two characters who are animals that can shapeshift into humans. One is a lion, the other a spotted hyena. Both have grown up with their respective animal species and only recently gained the ability to become humans. My question is, both lions and hyenas can do some things that seem very cruel from a human perspective. For the lion, since he's a male, he'll be trying to get established as a pride male, and he'll kill any young cubs belonging to other males. For the hyena, she has a twin sister, and very young hyena cubs have vicious sibling rivalry right after birth, which she mostly won and ended up being bigger and stronger than her sister as a result. Both lions and hyenas will also steal kills from weaker animals such as cheetahs. How do I portray this natural cruelty without turning off my readers and making them dislike these two characters?
You can portray their cruelty and natural survival tactics as in-depth as you like, but take time to highlight their positive characteristics if you want most readers to like them. Research some behaviors of lions and hyenas that can effectively be portrayed as kind or caring. At the very least make them interesting-I often enjoy cruel characters if their segments are fun to read.
Animals and humans are alike in ways where our personalities clash. I would try to look up Symbolism of Lions and hyenas. It will give you very useful information.
Perhaps touch upon it, leave it as implied without going into details, or imply that the characters aren't entirely remorseless and perhaps don't necessarily have choice in doing these things? "The pride was now his. The tough battle was won. Now all that was left was the nasty business. He looked around at the lionesses and their cowering cubs. He knew what must be done..." sorta thing.
This actually depends on the tone you want the piece to have. If the animals-turned-human are just for symbolism, it's acceptable to omiss some of their abhorrent in favor of the known, positive ones (like courage for the lion). However, if you go for a more genuine exploration of these unorthodox characters, ignoring the "messy" parts would be immature. These insticts are a part of their nature and shying away from them is shying away from what/who they are.
So, you want to be true to their primal instincts and yet want the readers to somehow relate or at least care in some way about the characters. Speaking of Hyenas, they also start devouring while their prey is still alive. A pack of hyenas is very well organize while hunting; they chase their prey by taking turns in leading the chase thereby saving energy and very effectively tiring the prey. My point is that as long as you show both aspects of their character you are fine. Sibling rivalry (specially to get their parents attention as a child) is not something your readers are unfamiliar with. Also, your characters are now humans as much as they are hyenas or lions, they are bound to be influenced by human ways in time. Show the progression/change from very beastly instincts to a much tone down nature influenced by civilizations/human, your readers will enjoy the ride and may be even fall in love with them by the end of the book.
I agree with kill bill, showing a progression would be best. Have them confront their actions, and question the morality of what they do. One of the things that separates humans from animals is their ability to question their own actions and examine their conscience. Readers should be able to empathize with the guilt and questioning; you could even turn it into a sort of "coming of age" story where the lion/human has to decide which aspects of themselves they want to preserve and which they want to change.
Depends if you wanna make them simply interesting, or if you want your readers to "like" your characters. Just because your readers may not "like" your character doesn't mean he won't be interested, which means, yes, your reader will continue to read despite characters he may not enjoy, but find absolutely fascinating. Perhaps making them slightly alien is your best advantage. Have you read Perfume by Patrick Suskind? The main character is a murderer and the author even depicts the guy killing innocent young virgins in quite cruel ways, and yet he was one of the most fascinating characters I've ever come across and thus, I could not put the book down. But did I like the MC? No.