Trying figure out what this weed is
The plant with the largest leaves in the first 2 photos looks like jimsonweed (Datura stramonium). It is poisonous if ingested. The flowers are funnel shaped and can be white to light purple. It is in the nightshade family along with tomatoes, potatoes, and many other edible plants.
Read more about it. http://extension.umd.edu/hgic/jimsonweed
The third photo has a few different plants in it. The one with the largest leaves appears to be pigweed. It is very common in agricultural fields.
Read more on pigweed. http://extension.umd.edu/hgic/pigweed
For both of these weeds, it is important to remove them before flowers and seeds form, if possible. The jimsonweed appears to have recognized the Roundup judging by the yellow leaves. You may need to repeat the application and maybe add a sticker-spreader to help it stick to the glossy foliage. If you don't have many of these weeds, manual removal would be advised to avoid damaging your soybeans.