The boring answer is tigers won't attack humans if they're smart, so it's not a danger.
Like most animals tigers have an innate fear of the unknown, which humans represent. Their instinct will be to avoid humans because they don't know what the humans are or whether they are prey. The fact that humans are tall (due to standing on two legs) will likely cause most animals to misjudge the threat level of humans as more dangerous then we are physically. Only very hungry tigers will attack the humans at all.
Then you throw in the ability for these humans to create more unknown scary things and you're pretty safe. A single fireball is all you need to 'defeat' the tigers. It doesn't have to even hit them, it's Fire! All animals are afraid of Fire, Fire is very dangerous in the wild! When these unknown huge possible-predators respond to your presence by flinging something as dangerous as FIRE at you, and you have no way of knowing that this comes in limited supply, you do not get closer, you run the other direction fast!
Put simply the humans are too scary an unknown for tigers to hunt them if they are smart. Part of being smart would of course mean making sure they don't look like attractive targets to a tiger hungry enough to be willing to take a risk (which as other pointed out your tigers would be pretty hungry). As such there are a few simple steps they need to take, but if taken they should be fine.
I'll also point out that tigers are a solitary species. As such humans would only have to worry about 1-3 tigers at once, depending on whether a female & male share a territory and if they foolishly set up camp right at the border of two males territories. Kill or, more likely, scare those few tigers into not dealing with you and you're safe.
1) don't go anywhere alone. Stick in groups of two or three. Most prey species institutionally are drawn to single animals, especially animals they identify as a herd species (which your novices are and the tigers may have realized by seeing their 'herd' working together). By having a few together that instinct to attack the isolated straggler isn't started. Furthermore if the tiger does attack one the other can fireball to scare it away before it has time to land a killing blow.
2) Keep fire at the base camp! A few simple torches around the base camp, or even a large camp fire with the novices intentionally sleeping with their backs to a wall/cliff/ocean and fire between them and the rest of the jungle, will keep any predator from coming close during night, or even day. If we presume their novice abilities give them some extra talent with controlling and feeding a fire keeping one up and running all times may make sense, or using small torches when hunting for supplies.
3) Teach the tigers to be afraid! Go out of your way to scare tigers whenever they come close. Throw a little fire at any nearby (maybe not enough for a 'full' fireball, just a small fire is enough). Maybe just light up a few touches and walk towards the tigers in a group with touches slowly, enough to scare them away but not enough to trigger them to feel they need to fight to defend themselves. Even simpler, just throw rocks at them, they won't fully understand how the rocks work and it can still be scary to them, particularly if you're somewhere 'defended' by a large fire burning you can throw projectiles at them without risk of their attacking. The net effect is the tigers will learn to stay away from you fast.
4) Find or build fortification. Pick a safe water source and create a camp there. Put logs or rocks down to make it harder to come up towards your base camp. If they have a means to cut down trees cut them down around your camp, to fuel the fire you keep running and to create a clearing so it's harder for things to get close to you. Failing that find a spot that is easily secured, a cave, a cliff face you can put your back to, anything that lowers the areas that these animals can come close to you at.
In all honesty it should be relatively easy to keep normal tigers away from the novices, with food and danger of death from exposure being the real threats. If you want the tigers to be any kind of threat the best way is to ensure they are hungry (though you still need to widen your island, as pointed out that many tigers in one area is just unbelievable). If you suggest some recent drought or other effect killed off some of the prey so that the tigers are hungry you could potentially have tigers hungry enough to be willing to take a risk by attacking humans. But frankly I think realistically your going to have to put more creativity in justifying why the tigers would be a threat to humans given their instincts to avoid us then why humans can't defend themselves against tigers.