How do I get family members to access my iCloud account?

If you want to share an iCloud storage plan, see instructions in Share iCloud+ with your family - Apple Support

Note that this does not enable them to access your data. See the following from that same support article:

When you share an iCloud+ subscription, everyone in the family group uses their own account. That way your photos, documents, and other information stay private, even though you're sharing access to the service. You simply share the features and space available in iCloud+ with your family members, so you only have one plan to manage.

You can elect to share some iCloud data, whether or not you share an iCloud storage plan. For example, see: How to use iCloud Shared Photo Library - Apple Support