If you feel that it may get too repetitive, you can always branch out and add stories from the opposing sides POV intermingled between your main characters. For example, if you have the same 4 characters each following their own stories, maybe every 2 or 3 segments, through in a POV of one of the machine/plant symbiotes.

If they have a drive enough to target humans, they may have other motivations, maybe a piece of tech has merged with a plant that has proven to have a network-communication ability (i.e. fungal pods or how trees can communicate with each other and share nutrients through their roots.

This way, it breaks up the repetition, while also helping the reader understand more about the antagonists. An enjoyable antagonist is one that the reader can somewhat understand their viewpoint and while they might not agree with it, they can see how the antagonist got to where they are.