Horse wont take bit

my tb can tolerate a mullen mouth or a three piece snaffle (though prefers mullen bc there's less moving) as he is extremely sensitive and has a very low soft palate.

I tried a snaffle once and he reared and freaked out. Figured out a simple loose ring snaffle wasn't mild at all on him due to his mouth conformation!

I thought about trying a mullen mouth bit, but from being forced to use a bit in the past, we're still trying to get over a total fear of the bridle. I haven't ridden much thanks to weather and not having time, so we're still working on her realizing that nothing is going to go in her mouth when I come near her with the bridle. She'll stick her nose right into her halter like a good little girl, but if she sees her bridle, it's head up, ears forwards and eyes huge, occasionally some snorting. She's started putting her nose in it for me though after she realizes I'm not going for her mouth.

If it is not and issue of teeth or bit severity. You could try some molasses on the bit. I seen at a seminar for parrelli, the speaker was using molasses in a generic style sqeeze bottle. He started by rubbing some on the horses gums and waiting, for it to discover the taste. Once the horse did that he put some on the bit. Now he can get the horse to even take the bit with him sitting on the ground. I thought this was amazing.