How are carbon-14 isotopes formed?

Carbon-14 is only one form of carbon; others have differing mass numbers, e.g. carbon-12, carbon-15. Thus it fits the definition of an isotope.

Isotopes are chemically same but physically differ, carbon-12 and carbon-14 have different numbers of neutrons so have different mass numbers.

Carbon-12 has 6 protons and 6 neutrons. Isotopes of an element have different numbers of neutrons. So:carbon-14 has 8 neutrons and 6 protons.

Yes, as clearly noted by the fact it is called carbon-14.

The daughter isotope of carbon-14 is carbon-12. The stable form of carbon.