Visa type and fund

[yysummer]

My mum and my grandma are going to visit me. They only have pension goes into their account every month. All the savings are in my father's account. Could they use my father's saving to sponsor them? Or both of them have to have savings under their names?

If they cannot use my father's saving, my husband can sponsor them. My husband has ILR, so my mum is qualified for family visit. How about my grandma? Family visit or general visit?

My mum is going to stay for 6 months, and my grandma 1-2 months. What's the minimum fund requirement to sponsor them?

Thank you.