Hi @Lily,
As it seems you are aware, a central requirement to bring family members here is that you earn enough to support yourself and them. This includes having sufficient living space for them and also that they have health insurance. If you feel you earn enough for this, they can apply for a visa with the German Embassy to come and live in Germany as your family members.
For your mom or grandma to come, they will have to prove that they are in an extremely difficult situation. Most commonly, this would be the case if family members were seriously ill, did not have anyone in their home country to support them, and their home country was not providing them with the healthcare they need.
Here is the relevant law for such cases, paragraph 36, section 2 of the Residency Act:
https://***.gesetze-im-internet.de/englisch_aufenthg/englisch_aufenthg.html#p0830
Let us know if you have any further questions.
Best,
Éanna