I think the weed killer in the fertilizer may interfere with the grass germinating. It's generally safe to use on lawns, but only after they're established. It's kind of late to try to seed a lawn, anyway, so maybe your best recourse is to try to get the weeds under control between now and when the temperatures start to drop and reseed then. The best time to reseed is probably sometime between August 15 and September 15.

Thank you for your reply. Trust me, I'm not using a lawn company anymore. I was planning on doing it myself but it was recommended by a family member that I use a lawn company. Now I know that was not a good choice. I actually spoke with a service manager today and he told me they would replace my sod if it dies.

when we moved into our new home many moons ago I did the same thing. I had a spray pump for Roundup grass and weed killer and a separate one for weed killer only... well guess what I grabbed the wrong pump in the next morning I woke up with round dead circles of grass in my front lawn wherever I sprayed it. It took a while but basically I raked out the dead grass overturned the soil a little bit here and there put some starter fertilizer and seed and it did come back. It took a while with some watering but it did come back that season. It's a good opportunity to put in some nice quality seed and end up with a very nice lawn. Perhaps you can rent a mini tiller or something and just to loosen the top inch or two of soil so you don't have to do it by hand and other than that put the seed down, fertilizer and water and I think you'll be fine.

Unless you are opposed for religious reasons, this is exactly the type of situation that roundup was invented for. One sprayed on dose and you can start seeding the next day. IMO, it would be more environmentally friendly than slowly solarizing a big area. You save all the benefitial insects and microbes and you can plant your wildflower crop immediately. The long term impact of a 1 time application of roundup is just about zero. All that plastic you buy to cover that much area will be with us for thousands of years. If you are absolutely opposed to roundup, you might try vinegar on a hot day. It will probably take a couple tries, but it does kill cool season grass.