You can't join a family group or set one up with a PC or an Android device. In Set up Family Sharing Apple is specific about membership of a Family Sharing group: To use Family Sharing, you need an Apple ID signed in to iCloud on an iPhone, iPad or iPod touch with iOS 8 or later, or Mac with OS X Yosemite or later [ie. macOS 10.10).
However, if part of the hardware in your household is a Mac you will be able to set up yourself on it with a user account, create an Apple ID, sign up to iCloud and administer the family group from there. The family organiser must be 18 or older, so it has to be an adult.
As your children already have Apple devices it's possible they also have an Apple ID (See Family Sharing and Apple ID for your child). Just make sure they each have their own unique ID.