Greetings likerallyk,
In order to have a family subscription, you'll first need to ensure that you've set up Family Sharing: Set up Family Sharing
Regarding paying for the subscription, check out the info below:
"About billing for Apple subscriptions and media products in India
To continue enjoying your subscriptions, you can add funds to your Apple ID balance.
Regulatory requirements in India apply to the processing of recurring transactions. If you hold an Indian debit or credit card and you have a subscription, these changes impact your transactions. Some transactions might be declined by banks and card issuers.
To continue enjoying your subscriptions, you can pay with your Apple ID balance. You can add to your Apple ID balance using App Store Codes, Net Banking, and UPI." About billing for Apple subscriptions and media products in India
We hope this helps!
Sincerely.