Tesla designs these so unless the installer messed up, they are all standard width. Don’t pay attention to any current striping. In fact, if you count stripes, there are probably more existing stripes than stalls which means they are WIDER than the existing spots. Here are the plans which show you how wide each spot is. Tesla has designed tens of thousands of these and know how wide each spot needs to be for their cars.
pg 3 is the demo page which shows the existing striping. Note that the SC stall in the left will be off the page so you need to account for 1 more existing spot. 8 spots in the demo drawing plus one more to the left equals 9. 9 existing to 8 new.
Pg 4 is the new Layout and you see the each stall is 10 ft wide by 18 ft long from center to center. Subtracting the width of the pedestal, you have at least 9ft width. Overall width of Model S including mirrors is 86”. 108-86=22. That’s about 1ft on either side.