1.You shall use Instant oats, if Rolled oats isn't available.
2.Do not skip the flavorings as they not only impart nice aroma but they act as pain relievers too.
3.Butter can be replaced with coconut oil. Do not use more than specified as more fat will soften the biscuit.
4.You can replace banana with any sweet fruit that is your baby's favorite.
5.You can place the biscuits in a zip-lock cover and freeze it for a month. You can directly give it from the freezer as cold bite will soothe the teething pain.
6.I am not sure if you can get the right hardness without oven on stove-top methods.
7.Teething biscuits are not for eating purpose and so it should be made hard enough that the babies shouldn't be able to break it. But, still it is edible. Babies will just suck it, gnaw it & eat the slight crumbles that disperse out. At any time, the biscuit shouldn't break into baby's mouth causing choking hazard. Biscuit will soften when it soaks for longer time in baby's saliva and the chances of breaking increases. That's why, store-bought Teething biscuits clearly mention to get back the biscuit from the baby after 20 mins of usage for safety. But, I have given this to my baby, 1 biscuit a day. She gnaws for 30 mins and then throws down. Then after sometime, she asks for it & gnaws for some more time.. She has used this for 3 hours in a day & none of the biscuits broke.. After first 30 mins, I always make sure that I keep observing her very keenly so that I could take off the biscuit immediately, if it breaks. Luckily, none of my biscuits broke. Do not give this biscuit, once their teeth is out as teeth could break the biscuit and also, longer stay of food particles in the teeth might cause tooth decay. This biscuit is only when they are teething & the teeth is not completely out, yet.
8.Do not store the used biscuits & give it again on the next day. Discard the biscuits on the same day.
9.The babies will drop the biscuit down and again put back the wet biscuit in their mouth. Some store-bought Teething biscuits use band to tie the biscuit to baby's wrist to avoid falling down in the floor. You can try that concept by putting a hole in the corner of the biscuit, before baking it & tie a soft band using the hole & tether it to baby's wrist. But, I just recommend to keep the floor clean. Dropping down and putting back in mouth will just increase their immunity ;)