Possibly the different types of trolls could be members of the same species at different stages of life. Trolls could change their appearance radically between each life stage, the way caterpillars turn into butterflies, as well as suddenly growing much larger each time.
Note that a typical human will grow about four to six times taller during their lifetimes, and some have grown much more than that.
A newly hatched crocodile might be only one foot long and grow to be 15 times as long and about 3,375 times as massive.
Newly hatched sauropod dinosaurs would be curled up in their eggs before hatching, and still could not be more than a few feet long when hatching, judging from the largest known dinosaur eggs. But depending on their species, they might grow to be more than 15 times, longer. A four foot long baby that grew to be 80 feet long would grow 20 times longer and 8,000 times as massive.
And some Sauropods grew much bigger than that.
If the legendary and controversial Amphicoelias fragilimus and bruhathkayosaurus were as big as the largest estimates, adults could possibly have been forty or fifty times as long as newly hatched juveniles.
So it is easy to believe that the different stages of the troll life cycle could be less different than tadpoles and frogs, and range in height by a factor of only four or five.
Note that many human children can walk and run well by the time they are two feet tall, and the tallest human was almost 9 feet, or 4.5 times that tall. And there was allegedly a prehistoric man over 11 feet tall judging from his leg bone.
The tallest living and prehistoric bears could rear up and walk on their hind legs for a time, at heights of 10 to 15 feet.
The extinct ape Gigantopithecus blacki is sometimes believed to have been bipedal and 10 or 12 feet tall.
A large elephant can rear up on their hind legs and tower about 20 feet tall.
And a large circus elephant was taught to walk on his hind legs for hundreds of feet.
Prehistoric giant ground sloths could stand up to a height of about 20 feet, partially supported by their powerful tails.
Thus if the trolls change their shape a bit every time they morph into a larger stage of life, they can have a size range much larger than you probably need.