Redrooted Pigweed?( Amaranthus retroflexus?)

So these are growing all over my father-in-law's garden, and he just planted pumpkins, and he is pesticide trigger happy individual and wants to spray everything. Even suggested putting jars over the pumpkin sprouts and spraying round-up around them.(absolutely horrible idea and mindset) I was trying to identify them and see if perhaps they were more beneficial than he supposed. I think they are redrooted pigweed (Amaranthus retroflexus), or related to Amaranthaceae family, but I am not sure. If so, I thought I read they were edible greens for raw salads or good cooked but I wanted to have some other opinions so I left some photos as attachments. If anything they seem like they would be a good mulch plant. My goal is to hopefully sway him into the direction of permaculture, especially since he recently bought 100 acres and plans to have some vegetable gardens, cows, chickens, maybe a pig but its hard to break that mentality. Your suggestions or replies would be most welcomed. Thanks.

I think you nailed it: looks like the old redroot pigweed to me. are the roots and lower stem on young plants red?

the greens are crisp and tasty when real young. a little older and they need some work.

there was a Korean gentleman who used to spend around 8 hours/day for two or three weeks on end every summer picking pigweed where I used to farm. we had to convince him to pull up the plants after he cut off what he wanted. he was hoping it would grow back. we were not. I was never able to convince him that I wanted to try some, but the impression I got was that he pickled then dried the leaves. he literally filled his car with large plastic bags full of leaves. he was completely surrounded by bags when he left for the day. chain-smoked the whole time, too.

a friend from Cameroon mentioned that folks in a region near hers cooked pigweed like njamma jamma, if that means anything to you. as far as I can tell, everything this friend has ever made for me was entirely new to my palate and very delicious.

goats like it. pigs like it (surprise).

it isn't the same species as grain amaranth, but the seeds might still be worth harvesting. likely not a quick and easy project.

grows fast, so it can add a lot of organic matter back to the dirt. a substantial portion of that will be in the form of seeds, though.

roundup won't stop it. it's a weed of cultivation. if your father-in-law wants it to go away, he'll have to stop turning or tilling the dirt.

a sharp hoe easily cuts the stem just under the dirt.

Eat it. It tastes better than spinach and is actually is more nutritious.

it's good for animals, too. It's leaves have 20% protein, which is pretty close to the protein level of alfalfa.

a couple of links that describe some uses.

this one is the same species: plants for a future

this describes some other Amaranthus species, but I imagine A. retroflexus could be used in many of the same ways: wikipedia