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This article will give you great info on herbicides;

https://www.gardeningknowhow.com/plant-problems/weeds/using-herbicide-in-gardens.htm

There are many different ways to control weeds. Close mowing, mulching, putting down rock or pine needles, choking them out by using a garden fabric, or sprinkling corn meal. Vinegar is a natural weed killer and used with epsom salt and blue dawn dish soap can combat weeds. The mixture is 1 gallon white vinegar, 2 cups multi purpose epsom salt, and 1/4 cup blue dawn dish soap. Make sure not to spray it on your plants as it will kill them. Good Luck!

Here are a couple of links with a few ideas. Using kerosine and gasoline is extremely dangerous and would not be recommended.

https://www.gardeningknowhow.com/special/organic/homemade-pet-friendly-weed-killer.htm
https://www.gardeningknowhow.com/plant-problems/weeds/how-to-kill-grass-naturally-kill-unwanted-grass-in-your-yard.htm

Working to remove weeds and prep an area for a landscape project is very important.
This is often the least 'fun' part of a project and is easy to talk yourself out of the work.
In the long run, and the beauty of your future landscape project, don't skip the prep work.
And very kind of you to help out a neighbor!

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/how-long-does-weed-killer-last-in-the-soil.htm
https://www.gardeningknowhow.com/special/spaces/soil-for-rock-gardens.htm

Unfortunately the weeds have to be pulled out of your vegetable garden to safely remove them.

If the soil has been watered it can make the task easier. Remove the entire roots and often times you will need to dig out a long tap root.

Use mulch to help smother the weeds from returning.
https://www.gardeningknowhow.com/edible/vegetables/vgen/vegetable-weed-control.htm

This link has more information on the effects of salt on soil and plants.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/sodium-in-plants.htm