As the data room owner, you can set the Default Guest Permission to follow a group's permissions.
When new guests are invited, they will be added to this group by default. This will happen when:
The data room owner approves a request from someone to access the data room; or
The data room's Access is either "Only people from domains I specify" or "Anyone with the link (email verification)". When a new guest accesses the data room, they will be added to the group by default.
To change your data room's Default Guest Permission, please refer to this article.