Hi. At four weeks your bones haven't fused together yet. It generally takes 6-7 weeks for the bones to knit together. My air cast forced my weight to the heel so not much pressure was on the fore foot. I actually requested it because I couldn't walk on my heel otherwise...too much pain. I had to wear one boot and can't imagine two. I called it my 'ball and chain.' My nephew called it my Frankenstein shoe and that's how I felt when I walked.
More power to you for having both feet done. Every doctor is different though, so maybe he'll let you try to wear sneakers. Good luck and let us know what happens.