This situation, with limited facts, is not cut and dry.
At the end of the day, the decision to file a form 1065 for this activity rests in your risk tolerance.
Should any of the 3 siblings get audited, you open the door to the IRS questioning this activity. IRS agents run the gamut on how they would want to handle this; correctly or incorrectly. Regardless, this is time, energy and $$ spent by you to maybe prevail.
The revenue procedure you are holding your hat on, is just some brief internal commentary on when the IRS would entertain a ruling request.
There are numerous cases and the IRS always refers to the fact that a partnership for federal tax purposes is “broader in scope than the common law meaning of partnership, and may include groups not commonly called partnerships.”
The IRS will most likely take the position that co-owners actively and jointly pursuing a business activity are deemed a partnership for tax purposes.
Not trying to create a panic, but the penalties for not filing a timely partnership return and related K-1's can be costly.
The other issue you are facing is the fact that you have not filed a form 1065 in the past.
So depending on your risk tolerance, you can continue down the same path, or file a form 1065 that you indicate you are essentially completing already. At some point, this will certainly close the statute of limitations on some of those "open" tax years.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
