Here's your nichelings' pet ratings:
Anala would be a good pet, but needing to be brushed daily and after a walk to avoid matted fur. She'd also need to be taught to not ram people early on. Good first pet but requires a lot of attention.
Lenla would certainly be a bit more of a handful, with more dangerous horns and a digging paw. Would need constant supervision if unleashed outside, as she can and will dig several holes (and you will be fined if she does this at a park), she will also attempt to dig indoors if she doesn't get to go outside often enough. I recommend giving her toys she can bat around, blankets can be good toys for digging but tend to be ripped to shreds. Like Anala she will need to be taught to not ram people. Would not make a good first pet, good for an experienced pet owner.
Inana would be a terrible pet for children due to her venomous fangs. Needs to be taught to not bite early, has to be handled with gloves to ensure to accidents, go to the hospital immediately if skin is bitten. Her water-oriented genes mean that she needs regular swims to live a happy life, so some sort of swimming pool is in order. Keep in mind that chlorine is harmful to nichelings. Not suited to be a pet at all, will be happier in a zoo or a reserve