These fans appear to be 3-pin, voltage-controlled fans.
Your CASE_FAN headers needs to be either 3-pin or 4-pin with backwards compatibility (3-pin will work, but 4-pin from mobo is uncertain).
*I would actually just connect them with the 4-pin MOLEX and run at a constant speed using the 7V adapter.
(should be plenty of cooling, and quiet enough not to benefit from fan control dropping lower)
Otherwise, it looks like what you're asking about is a 3-pin fan splitter. Might as well get 4-pin as it's backwards compatible:
https://www.amazon.com/SilverStone-Technology-Sleeved-Splitter-CPF01/dp/B00B46XKKQ/ref=sr_1_1?s=pc&ie=UTF8&qid=1467610262&sr=1-1&keywords=fan+splitter
I could be wrong, but do you only have ONE fan header aside from the CPU's?