Payment integration to charge all registrants as required

Hello all!
I’ve got a client who’s interested in building a membership website for a funeral committee. The way this committee operates is that along with a registration fee, anytime a member dies, all registrants are charged a specific amount to cover the costs of the deceased. This amount charged will inc/dec depending the number of members, and the charge can occur at any time.

With this being said, I am looking for an integration/software which works with webflow that can:

  1. charge a one time registration fee
  2. give the client the ability to charge all members as required
  3. give client the ability to choose how much all members are charged.

Any and all suggestions are greatly appreciated!