Speaker set up for more than 1 person

I agree with Spenav. What you're trying to achieve is fundamentally not possible. A true center image is only possible by one listener sitting precisely between the speakers. Set your speakers and chair up just for one person and then don't tinker with them!

It’s all about compromises with your system.  I would adjust the toe-in or out and go with whichever sounds the best trying several listening positions.  Then move back to where it sounds best when it’s just you.  I put painters tape on the floor to mark the positions so it’s easy to move the speakers’ back and forth as needed.  

Need to know your speakers. 

As others have said, it's physically impossible with a 2 channel system to have a sweet spot big enough for 2 people sitting normally. I would run a center channel when you have guests over or even for yourself on some music. This way you trade holographic (stereographic) imaging for pinpoint center, flat image. Soundstage can become overly grand but with the right music, the right mood, it's a fun time.

EQ/DSP will almost surely be necessary. Here I would ignore tonality problems and prioritize an even bass response across the sofa

My Sweet Spot is about  + - 5 in. on X axis and 3 ft. Y axis. Speakers are Maggie 1.7i s so Y axis SS is much greater. Wife enjoys the sweet spot too, but is usually content sitting to the side out of the range.

For her to best enjoy her favorite songs, my solution is for her to sit in LP and I sit in LP on floor with her legs on my shoulders. What can I say, it works for us. Of course this position wouldnt be best with friends, lol.