How do I achieve these skill kills as it is the only 2 I am missing from the list of skill kills & any pointers would be apreciated, thank you..?

I'm right their with ya i havnt gotten any feedback or found any info on what you have to do.

Relentless!: 4 Kills in rapid succession

Psycho!: 5 Kills in rapid succession

Tips:

-Play Crash Site.
-When deploying your Orbital Strike, make sure you can get a few kills without it directly afterwords.
-Take your time, wait for enemies to bunch up before attacking.
-Try lobbing a 'nade in a group of enemies first. Might not result in a 4-5 kill, but it will get them softened up for the shooting.