Your plan might work since your guavas are relatively large. I once tried separating two seedlings growing together in the same pot. They were not very old, under a year probably, and smaller than the guavas in your photo. Unfortunately, my efforts at separating them ended up killing both of them.
One thing to note is that, based on what I observed with my two seedlings, the root balls are intertwined with each other; some of the roots belonging to the plant on the right (in your photo) will be growing on the left plant's side of the pot and vice versa. When you cut the combined root ball in half, you will be severing a not insubstantial amount of roots for both plants. But, I think you will still be able to successfully carry out your plan as long as you are able to maintain two intact root ball halves and do not lose any dirt in and around the roots in each half. That way, each plant's remaining roots will not go into shock from a lack of dirt and moisture, even though each plant has lost some roots. I think that is what went wrong when I tried to separate my two guava seedlings; each plant was basically bare-rooted from losing so much dirt, in addition to losing some roots.
That is my two cents, anyway. Good luck.