Sightreading is a lot about pattern recognition. The more patterns you can play without struggling and the more often you sightread these patterns, the easier things become. Once you're kinda fluent at sight reading, it's not really about "reading a chord". The chord itself is a simple pattern that you identify at the first glance - since you know it well - and then it's just about where to place your fingers.
Take something simple as an example: Just normal major chords (1-3-5). They're easy to read, aren't they? The same pattern of notes with the only difference being the base. If you practice these chords for a short amount of time, you'll have no trouble identifying what to play as you see the notes.
It's really important to start out simple. When you learn how to read in school, you don't start with Shakespeare. A prerequisite for sight reading is that you aren't struggling with the technical bits of what you want to play. If you do, the piece is too difficult. The key problem should be the eye-hands coordination.