I agree with FrostiesFishes.
Angelfish are a type of cichlid. Though that does not mean they are very aggressive, they can eat any fish that fits in its mouth.
There is not really any way to keep the angelfish from eating the neon tetras, even if you feed them well. You should be fine for about a year or so, but after that, you should remove the neon tetras if you want them to live.