On this Enpass Support Page it is stated that
As explanation there is a link to this Apple Support Page about Family Sharing on which we get the information that family sharing is technically possible with in-app purchases...
There are a bunch of apps that use family sharing subscription paid with in-app purchases, i.e. Fantastical Calendar or Halide Mark II Camera etc.
Why is Enpass stating that it is "technically not possible" though the decisive point is if Enpass wants to participate in-app purchases supporting family sharing?