Thank you so much for the extra photos. These chairs are American 20th century (circa 1920-40, yes, they even still make these today)
Windsor brace-back, slat and spindle chairs with rush seats. The numbers on the bottom indicate that they were made in a factory as these are
numbers for each part. The little bump in the back is the 'brace-back', a varied form of the Windsor chair that helped add stability. The set of chairs you have are valued at $100 each for the dining chair and $200 each for the arm chairs. I am going to add photos of 1780 Windsors (all I could find was a rocker, but same idea) so you can look at the arms and see that period chairs wither had 'knuckle' ends or had very thin planks of wood. Then look again at your chairs. You have very crisp-edged, thick planks of wood used and a serpentine arm. Also, the construction looks to be with screws and glue where older ones were pegs and tiny nail heads. The easiest tell is the condition of the rush, which looks original and the paint, which also looks original. If the chairs were any older than 1920, there would be more wear in common areas like this.
Here is a great article on the history of the Windsor;
If you are wanting to sell your chairs, Some sites that I recommend are Varagesale.com, Chairish.com, Ioffer.com, Furnishly.com, Deconet.com, Lushpad, Krrb.com, and letgo.com.
You can also go to invaluable.com or liveauctioneers.com and search their directory for an auction house near you and consign to them.
To finish, I will need you to click the five stars at the top of your screen and hit the submit button, thanks!