Application for multiple clients and users

I am building a simple app which is for organization membership directory. I am the owner of the application and multiple organizations should be able to use the application. There are basically 2 collections besides the users. here is the relationship
Organization - > 1 to many. Members
Organization → 1 to many Users
Members → 1 to many Users( But technically 1 user for 1 member) .

as an owner I should be able to create as many organizations. Each organization has its admin and regular users.
org admin should be able to add members with their information - name, address, phone email pic, etc.
A user could only sign up if he is added as a member of any organization.
I did the sign up as 2 parts, section one just sign up with email, password and full name. Sign up 2 screen has Member drop down and an automatic field for organization. if the new sign up user is a member of any organization , He will be in the drop down and user can continue . The second sign up screen submit button action is actually update user. If the user is not a member of any org, he will exit and the signed up user will be deleted .
I am successful except one thing. In the second sign up screen i get correct information for member if he is added as a member of any organization ( I use custom filter using email) . However In th automatic field for organization is not captured in the Signup process. In the automatic field → value I set as. Logged in users → Members-> Organization . But after sign up and user created, The Organization field in the user is empty . The signing up user has only one record in members and member has only one record in Organization. I should get this value , But not getting
Can someone help?

Is there any other method to implement this