Angel Fish

Angelfish are cichlids. Males are territorial and will not tolerate another male in 'their space'. With 4, there are several possible combinations of male and female.
Since two of them are picking on the other two, it sounds like you have a male and female that have paired up and object to sharing the tank with the other two. The two that are being picked on could be 2 males, 2 females or one of each.

I would move the two being picked on or they are likely to be killed. If your other tank is not big enough for 2 angels, you will need to find a shop, or another person to take them. If the tank is big enough the angels should leave the 3 small fish alone - unless they too are angels - but if the picked-on two also turn put to be a male and female which pair up and they then breed, they will attack any fish that goes near the eggs.
This also applies to the two angels that are picking on the other two if there are fish besides angels in the tank.