for bullet disappearing:
Someone else helped me with this too, go to bullet and set event "collision with (your boss object)" then in codes, you write "other.bosshealth-=1 sound_play(sndBossHit) instance_destroy()"
for boss attack:
you set it as the boss to move towards player, not the object. So you create a threat, let's say it's the fruit, you name it something like deliciousFruitMove, put the "move_towards_point" code in that object, and delete it from the boss's. Then in the boss's code, change the "instance_create(x,y,deliciousFruit)" to "(x,y,deliciousFruitMove)"
if you set the boss as solid, sure the bullet will disappear, but the boss won't count as hit, so its health won't decrease