1| Mixing and matching two different sets of ram kits will only result in instability. So the first point of duty is to not do it.
2| There will also be a limitation from either your chipset or your platform in spite of having 4 ram slots worth populating. So we can only answer that after we know your motherboard and your full systems specs.
3| Is it possible to pass on links/images to the two kits. Include their brands, densities, timings, frequencies and voltages.
4| A set is also dubbed a kit whereas a single from a pair of ram modules are called a stick of ram.