There are three small issues for you to pay attention to here, and you'll need to get a couple of accessory parts.
First, to use automatic control of speeds of your case ventilation fans you really should connect them to the mobo CHA_FAN headers. The other headers are designed for different functions and don't control the correct way.
Second, all four of your case fans are of the 3-pin design, and that means their speeds can only be controlled by mobo headers that are configured to use DC Mode, and not PWM Mode. See your mobo manual on p. 3-7. Check to be sure that each of the CHA_FAN headers is set to DC Mode by using the selector box at the upper right of the screen. If you have to make a change there, be sure to SAVE and EXIT.
Third, how do you connect four fans to two CHA_FAN headers? That's easy using Splitters. Any normal CHA_FAN header can supply up to 1.0 amps current in total to the fans connected to it. Most fans today use from 0.1 to 0.25 amps, so two on one header by using a Splitter is quite acceptable. You should realize that any fan header can accept from its fan(s) the speed signal from only ONE fan. Thus all Splitters are designed (usually with a missing pin or wire) to forward to the mobo header the speed signal (on Pin #3) of only one of its fans, and to ignore all others. Thus you will never see the speeds of the second (or more) fans on one Splitter and header. Now, a note on selecting a Splitter. You will need two - one for each CHA_FAN header to connect two fans to it. It does not matter whether the Splitter you buy is designed for 3-pin or 4-pin fans, either design will work for you. But what DOES matter is distinguishing between a Splitter and a Hub. Unfortunately, there are many Hubs sold under the name "Splitter" that do not do the Splitter job properly. A Splitter has one arm ending in a female (with holes) fan connector that plugs into a mobo male (with pins) header. Then it has two (or more) arms each ending in a male fan connector that you plug into the fan's connector. Here are examples
https://www.newegg.com/Product/Product.aspx?Item=9SIA3XT1D86510&cm_re=fan_splitter-_-9SIA3XT1D86510-_-Product
https://www.newegg.com/Product/Product.aspx?Item=N82E16812423160&cm_re=fan_splitter-_-12-423-160-_-Product
The first is a 3-pin type with wires exposed to see easily. Note that the second output arm is missing the Yellow wire to its Pjn #3. The second Splitter is a 4-pin type with black sleeving. Both would work for you. Ones with longer arms also are available.
A Hub is different. It has those arms PLUS one third type of arm that ends in a connector that must be plugged into a PSU output (either a 4-pin Molex female or a SATA Power Output). This device type can only work with 4-pin fans systems, so they are NOT what you need.
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