It appears that your grand father had a license for selling veterinary medicines and hence the license would have been valid upon demise of your grand father and till the time of expiry of tenure of licence.
However it appears that the tenure of license had expired and your father did not renew the same.
Normally for persons who did not apply for a license of willfully defaulted in renewing the license,Clause 27 b (ii) of Drugs and Cosmetics Act will apply and penalty is that an imprisonment for a term of less than 1 yyear and a fine of not less than 5000 rupees will be applicable.
However in your case it is evident that
a) Your grand father had a valid license and the tenure of license expired
b) that you were selling medicines that are genuine and not spurious and
c) you had a pharmacist license in place and upon death of the existing pharmacist, you opted to hire a new pharmacist.
d) Also your father has been a regular tax payer and has been paying taxes goes to show that the non renewal of license is only a mistake and not a fraud.
so all of the above will show that your father is not a willful defaulter and hence the court/ department will direct your father to pay a fine amount only. No jail sentence will be awarded in your case.
All you need to do is that non renewal of license is neither willful nor wanton, but a mistake of fact and not law.
Jail sentences will be applicable only if you have sold spurious medicines and indulged in other criminal activities in addition to non renewal of license.
Hope this information is useful.