Well I am a member of an S Corp that operates as a partnership. I depends on how the business was set up. So I stand by my statement.
We did not get much information from the question. Only that its a DBA and one sister gets 90% and the other gets 10%. As a partnership they would file Form 1065.
An S Corp operating as a partnership would also file Form 1065.
The BDA could be a partnership or an S Corp.
