It depends on the type of entities in the brother-sister group of entities. 

Under the SBT, controlled groups and entities under common control were generally defined to include situations where the same five or fewer unrelated individuals, estates or trusts owned a controlling interest in two or more entities taking into account the ownership of each such person only to the extent such ownership is identical with respect to such entity.  See, e.g., RAB 1989‑48.  However, under the MBT, a unitary business group is: 

a group of United States persons, other than a foreign operating entity, 1 of which owns or controls, directly or indirectly, more than 50% of the ownership interest with voting rights or ownership interests that confer comparable rights to voting rights of the other United States persons, and that has business activities or operations which result in a flow of value between or among persons included in the unitary business group or has business activities or operations that are integrated with, are dependent upon, or contribute to each other. For purposes of this subsection, flow of value is determined by reviewing the totality of facts and circumstances of business activities and operations.  [MCL 208.1117(6).]

The Department will follow IRC 318 or analogous authority to determine indirect, or constructive, ownership and control, except that the Department will apply IRC 318 to all ownership interests.  The attribution rules of IRC 318 vary depending on whether ownership and control is attributed to or from a corporation, partnership, trust, or estate. 

For corporations, so long as none of the five or fewer unrelated individuals, estates or trusts own more than 50% of the brother-sister group of corporations, or no two individuals, estates or trusts own 50% each, then the unitary business group control test under the MBT will not be satisfied.  Under IRC 318(a)(3)(C), a corporation will only be deemed to own the stock of any shareholder if the shareholder owns 50% or more of the stock in that corporation. 

Example:  Alice, Bernice, Carol, Donna, Eunice each own 20% of Corporations A and B.  Neither Corporation A nor Corporation B will have indirect control or ownership of the other through IRC 318 since none of the shareholders owns 50% or more of either corporation.  The MBT unitary business group control test fails. 

In contrast, for partnerships, so long as any group of individuals, estates or trusts own more than 50% combined of the brother-sister group of partnerships, then the unitary business group control test under the MBT will be satisfied.  Under IRC 318(a)(3)(A) as applied to the MBT, a partnership is deemed to own the ownership interests owned by any of its partners. 

Example:  Al, Brett, Carl, Dave, and Ed each own 20% partnership interests in Partnerships Y and Z.  Under IRC 318, Partnership Y indirectly owns and controls 100% of Partnership Z (and vice versa) since Partnership Y is deemed to own all the partnership interests owned by Al, Brett, Carl, Dave, and Ed (which totals 100% of Partnership Z).  The MBT unitary business group control test is met.