Most comments here ignored the kids’ preference to play on the iPad. With that in mind, you may want to check out the Realms offering. I believe you get a 10 user server for ~$7. Note that is also highly fragmented, and there are different realms subscriptions for Java and Bedrock and also different tiers.

Depends on what your goals are with the family server, Realms may not be a good fit at all. But in terms of getting kids playing together simply and quickly, it’s the easiest way to go.

As a side note, I know kids who switched to Java after years of insisting only on Bedrock and sorely regretted not making the move much sooner. This is part of growing up these days.