UK visitor visa for parents and brother

[Sathyabhama]

Hi,

I am planning to bring my parents and brother to the UK from India for 2 weeks for tourism.
I am Tier 2 general dependent. I am sponsoring​ their trip completely. My documents​ are clear.
To show the current financial and social status of parents and brother in India,
Brother is employed, has sufficient funds to manage himself.
My father is retired and gets government pension. He has his pension book and bank statements. Mother is unemployed and dependent on my father.
The glitch is that, my father doesn't have any balance in his account as he withdraws the pension completely and gives it to mother for household management.
Mother has a bank account in which she saves the extra amount remaining after months expenditures. This account has eventually piled up to a good amount.
I m worried that my parents visa might get rejected saying,
Father doesn't have sufficient funds in bank account. And mother is unemployed and has unaccounted fund in her account.

Please let me know what to do now. Will they get the visa by just submitting mother's bank statements and father pension book?
Should I ask mother to include father as secondary joint account holder?

Please share your thoughts.
Thanks.