more realistic bows

There isn't really an easy or straightforward way to do this. It's not impossible, but you'd need pretty extensive knowledge of ranged item mechanics, item states for different use durations, and some procedures to determine the accuracy/velocity of the resulting arrow based on the use duration. (As well as the inherent difficulties of creating a ranged item capable of using custom arrows.) For anything involving arrows, there will also be situations where you need to lock and manually alter the code of various mod elements to get certain stuff to work properly.

...And if you are replacing the vanilla bow, (which is still easier than changing the vanilla bow's behavior), it'll cause a host of other problems with vanilla loot tables, bow wielding mobs, crafting recipes, etc. If you do want to go through with this, I'd recommend making a new item, (call it a 'longbow,' or something), that uses your custom mechanics, distinct enough to be unique compared to the original bow.