How do you manage your wood with 2 different stoves? and other issues

Sounds like 15" pieces would work for both stoves.

I agree I would cut all the wood same length. 15 sounds like a good number. That way you don't have to worry about managing your stacks for two stoves

I would consider consolidating the two stoves to one central unit - furnace or boiler.

That's said without knowing anything else about your situation though...

I went with 16" as my number for upstairs and downstairs. I bought six extra firebricks and put them in my dragon (three to a side) to make the firebox "seem" a little more appropriately sized.

I don't process most of my firewood, I purchase it from 2 local guys who are pretty fantastic, all things considered. They both know I have 2 different sized stoves, and split firewood for me, knowing this (I recommend them highly to others, no complaints so far in 5 years )

The firewood gets delivered by the truck load, and I sort and separate it as I stack it. IE, I make a "13" pile and a "PE" pile, or as I sort it, one wheel barrow full for the 13, one for the PE, and move it and stack as close as I can to have easy access from both stoves. Luckily, for me, the stacks for each stove are only about 25' apart, so it's not much of an issue, I just take my time, and do about 4-6 wheel barrows full a day until the piles are gone.and all the wood is stacked, picking up the trash & the bark that falls off for kindling.

Both of the stack areas are under trees, but in an open enough area that they get plenty of air, and usually season pretty quickly. I don't top cover until fall.

I don't separate by species. I've found that even with seasoned firewood, you'll get some that just doesn't season, and will spit and sputter once it's put into the stove. That's where a piece or 2 of seasoned pine that's been mixed in with the stacks comes in handy.

That being said, I took down 2 oak trees, and have been processing them as I can. That split firewood is on pallets, and left au naturale. It'll season when it seasons. 2 more down in the back yard that have to be processed, and 5 more that have to come down.

Dix is gonna be a busy gal this spring & summer

I have the same issue. I have a big earth stove insert in great room and nc13 stove in my bedroom. I have slowly started to make my cuts the same length. It doesn't always work out when tree services drop wood off - I split wood with a few friends all have bigger stoves and want longer splits - its a mess for sure

You don't need sun exposure, it is just nice to take advantage of.
It's not in the sun at night and night is pretty long half the year.
I haven't stacked in the sun for 25 years.
I keep the pine, oak and even the maple and cherry separate if I have enough of it .
I've been at least three or more years ahead on c/s/s for two decades.

Sometimes I'll take the odd maple or birch and toss on a two year old short stack of oak to make it a cord because it will be dry by the time I get to using that stack.

I'm not always the most accurate cutter for length though I try for the length of my bar which is 16. Plus sometimes I cut with a group of people who cut 18. So I have a mix. Anything too long for the stove that takes 18 either stays in the stack (or gets returned to the stack) for the stove that can take anything that will fit through the hole in the top ( Tempwood clone ). I only pick by size for the TN19 (18" ), the bigger stove gets what it gets, basically fed whatever fits, short or long. ( Tempwood is sort of a bonfire in a steel box kind of stove ).

if you process your own wood, just cut to the largest length that your smaller stove can handle. i have a basement and an upstairs stove and learned that that lesson the hard way. in my situation, i much prefer running the basement stove because i like the buffer the floor provides and less dramatic temp swings... but the basement stove handles logs about 6" shorter then the upstairs stove. Sooooo... i when i pull splits off the pile, stuff that is too big has to go into another pile to either be only burned in the upstairs stove or cut down 4"-6". although if you pile a mess of those short cut off into the stove, she gets very happy. but honestly, its a pain in the butt to have to sort out your firewood off the stack, especially if you have to trim. i'm a year ahead so hopefully i finish off my long splits this year and can be done dealing with them.
for your second question, you don't need sun to season your wood. if your airflow is minimal, you want to only stack in single rows in order to utilize whatever breeze you get. personally I'm an advocate of top covers, not for the first year (or summer) for green stuff but i just feel it helps keep things drying during the wet months. if you have a lot of trees, use them as "ends" and stack between them. just put down a ground barrier like half a pallet or some 4x4's, whatever you got really.

Sell the stove you like less, and buy a second of the one you like more. I went thru the same debate when I installed my second stove, and this was a factor in deciding on a second of the same model. Parts interchangeability, and learning if factors unique to my original install were causing some of the troubles I occasionally had, were also big factors.