family member cant accept my invitation for 365 family sharing,

Hello, thank you for reaching out to Microsoft Q&A.

If you send a invitation link to your friends or neighbors to join the Office 365 Family Susbcripiton, they should accept the invite within 48 hours. If the link is not accepted with in the time limit, it will be expired.

So, try sending the invitation link through message or via email and ask them to accept the invitation link. If they are having problems accepting the email invite, try sending the invitation through text message.

Also, make sure you have not exceeded the sharing limits. You can share the Office 365 Family subscription upto 5 members. You can m anage your subscription in your Microsoft account here-

https://account.microsoft.com/services