Obviously we don't have full details of the injuries, but Walker's injury looked like a bad ankle twist - painful and debilitating in the short term, but shouldn't cause any longer term issues. Stones' injury seemed like a muscle tweak - inoccuous in the short term but with a risk of rumbling on (I wonder if it's the same issue that brought him back from international duty?). Especially given their respective injury histories, I'd prioritise giving Stones the full required healing time.
If Kyle's healed enough to be able to use his speed (his biggest weapon, and without it he might be a defensive and/or disciplinary error waiting to happen), I say strap him up, load him up with painkillers and start him. Best case scenario, he gets through it unscathed and plays himself into some fitness. Worst case scenario, he aggravates the injury or twists the ankle again, we have to bring on Stones or one of the kids (or do some awkward reshuffle from central defence or midfield to cover the position) and we're without him for another couple of weeks, during which time we miss him but we can use Cancelo at right-back, with Zinchenko and Ake as left-back options.
If Kyle isn't recovered enough to have his speed but John's feeling okay, then we can play John, but the risk is that he turns a minor injury into a major one and we lose him for the rest of the season with one of his protracted muscular niggles. All the while we have Ruben only just come back from a hamstring injury, and Ake got a knock recently too, so if luck goes against us and either or both of those players suffer a return of their injuries or just need resting in order to prevent further damage, we're suddenly very low on centre-backs.