How big is the tank? 4 Tetra *can* work with a betta, but tetras seem to be pretty delicate, so you need to make extra sure to have pristine water. Your betta will appreciate that too. A bigger tank should be fine, a smaller one...not so much.
The Boy Feesh: Indigo CT, Lavatail CT, Ghost CT, Chicory HM, Redfish VT, Magic DT
The Girl Feesh: Christmas CT, Shine VT, Snowflake CT, Stripes VT, Midnight CT, Grif VT, Tangerine VT, Wraith CT, Amethyst VT, Ice CT, Poe CT, Turquoise II CT