Knowing the exact model of the main speakers would help, they look like Quest/ReQuest. Also, have the panels ever been changed, and if not, how old are they (i.e. when was the speaker made)?
There are serial numbers on the speakers and panels we can decode for you to know the exact age of each.
The two ReQuest REKG029, and REKG028 - November of 1993
The two Script FEME044, and FSMF104 - May of 2001
The one Cinema TFMI010 - September 2001
As for value, as another owner of 1993-vintage ESLs (my rear Sequel IIs) on original panels, they might still play but likely have a serious HF drop-off. Room correctors can compensate, as that drop-off closely matches the default curve in Audyssey. Trying to play with a 'Flat' setting might overdrive your amps. So, as long they are used with the normal roll-off, the boost is minimal.
But, as a buyer, I'd seriously consider ordering new panels while one still can.
One way to understand value is to take a look at recent listings her and on other sites, like Audiogon.
Here's a search on our site for Requests for sale: Search results for query: Request
Looks like pricing for ReQuests is in the $500 to $1000 range. A lot will depend on condition and buyers proximity to you.
Given you have a complete set, try pricing it attractively if it is all sold together to the same buyer.
Many would love to pick up a full set, but shipping is stratospheric (and risky), so your buyer pool is likely people within a few hundred miles of your location. If I wanted those ReQuests, Kentucky is not too far for me to go.
The last I knew, an Audiogon membership, worth the money if you have big ticket items to sell, gave you access to an "audio blue book", with suggested prices. You can also check Audiogon or USA Audio Mart for ads for those items, though you might have to wait a while for enough instances to appear to get good data. For items like these, local pickup is simplest, but if you have the original shipping boxes it gives you other options, and adds to the value.