Several ways to go about completing this mission, you are suppose to sneak snipers past defenses up to the singularity reactors and shoot them to disable the desolators and the lucifer turrets, But frankly all you need is a single scythe that can walk along the mountainside and then along the top of the map to get to the singus. Your mission is to get your commander to the relic though so potentially you can skip this part.
All you need to get past the desolators is some slings to destroy them (build a radar) or a tough commander that can survive walking past them, plus you can shoot the energy pylons (with snipers) connecting the desolators to the singularity reactors.
For the lucifer you can swarm it with units to either take it down or keep it busy while your commander walks up to the relic, your snipers can take down the lighter defences like stardusts.
If you're having problems with the attacks from south you can just make stingers or any number of defences on the mountainside where they come through.
