Chartered Accountant's help needed

My father passed away 2 days ago. I am just 22 and was studying, never looked for his property or Income related things. Now, I am very confused about what to do.

My father had Income tax file and I found IT certificate for 2017-2018 and the income mentioned was a little less than taxable income. My father had fixed deposits in 3 different banks and all were QIS (Quarterly Interest Scheme). My father was about to retire from work after I get a job within 2-4 years, That’s why he chose this scheme. All FDs had my father’s name as first name and my mother’s name as second name. Mode of operation was Either or Survivor for all bank accounts.

Unfortunately I don’t know who my father’s personal CA was and I couldn’t any way to contact him. I remember him filing 15G form for all accounts in April as the income doesn’t fall under taxable income. Is there any way to know if He filed for income tax certificate for this year? Is there any way to retrieve contact of my father’s CA with the tax certificate available with me?

Now, some FDs are about to mature, Shall I wait for them to mature before closing my accounts? Is there a way to replace my father’s name with my name in bank account or will I have to create fresh bank account and withdraw the FDs prematurely? Remember all accounts are jointly held and mode of operation is either or Survivor. Please tell me if there is any way of tax deduction as I wouldn’t be able to file IT return on my father’s name?

Now, Shall my mother have to file income tax certificate as all the money was kept in my father’s name and suddenly a huge sum will be added in mother’s name or be linked to my mother’s PAN? Or shall I divide the amount to accounts of all three of us? My sister is going to be 18 in September this year and don’t have a pan card yet.

I will post other questions here when I remember them. I never cared for these things and It’s a sudden thing for me. I wouldn’t have asked this questions to you if I could contact my father’s CA.