Do individual members of a group exemption ruling have to file separate Form 990 returns?
The parent and subordinate organizations of each group exemption ruling must agree on their filing responsibilities. If the parent chooses to file a group return for some or all of its subordinate organizations, and those subordinate organizations agree to be included, then the subordinate organizations should not file their own separate returns. However, if a subordinate organization is not included in a group return, then it must file its own return unless it meets another exception to the filing requirements. See Filing Requirements for more details.
Publication 4573 , Group Exemptions