I hope your mother board have 4 RAM slots, if so, it will support, Dual Channel, trichannel, quad channel
Dual Channel Means: You should put TWO exactly identical RAMs in 1,3 slots OR 2,4 Slots, but both RAMs should be from Same brand, same speed, same capacity and same timings .... everything should be same
Similarly, Trichannel means 3 RAMs and Quad Channels mean 4 identical RAMs in 4 RAM slots
Dual Channel configuration increases RAM bandwidth by 2 times
Quad Channel configuration increases RAM bandwidth by 4 times
Evan if you have 16 GB of RAM, you have 1X8GB stick + 2X4GB Sticks = 16GB, with your 8,4,4 sticks you cannot configure any dual or tri channel, if you put all on mobo, then it will be only single channel.
If you put 2X4GB RAM in 1,3 slots or 2,4 slots, you can have dual channel configuration, with your current 2X4GB RAMs
Option1: So, you can sell 2X4 GB RAMs and get another similer 1X8GB and configure dual channel
Option2: Sell 1X8GB RAM and get other 2X4GB RAM sticks and have quad channel configuration
I hope you are clear
My Opinion: I think 8GB of RAM will be more than enough, so I recommend you to sell 1X8GB stick and keep 2X4GB with dual channel connection, if you need to increase the RAM in future, you can have another set od 2X4GB RAM and connect quad channel configuration,
Dual channel gives 2 times bandwidth than Single Channel
Quad Channel gives 2 times bandwidth than Dual Channel & 4 times bandwidth than Single channel