Hi Jkpita!
Well...I hope you have good knee-pads!

Cold winters huh....I wouldn't know...Fargo only got to -30 this morning; and I think Bismarck, ND got to -35+!!!
So, if Fargo hits 100 this summer, I can honestly say...where else on "G*ds-green-earth" can you have 130+deg. variation in ONE year...???
(I can't understand why there's movement in your structure?!!?)
;-)
Crikey!!!

Seriously though,
* I'd lightly scrape along the cracking/lifting areas with a putty-knife to see how easily it pops off.
* You've GOTTA get rid of loosely bonded layers, or your new paint will literally pull-off the old.
* I can't remember what it's called, but find some real dense/hard foam. Somewhat like the foam-insulation sheets.
* These can be trimmed to make a "sanding-profile" block that will follow your trims' curves.
* Or, just use flexible sanding-sponges.
* If you have sharp ridges, just use your putty-knife carefully to press the paper along these ridges, to help bring back any "definition-lines".

NOW-
When you're sanded-down to smooth/sound trim...AND all dust is removed...
* Haul out a good brush and primer!
* There's NO reason to use oil for ANYTHING here.
* 123 primer from Zinsser, C2-One by C2 are two very good ones. Ask at your stores what their best Latex primers are.
* If you're REAL fussy, you can lightly sand these primers, but you've gotta wait 1/2-a-day or so b4 they're dry enough to sand nicely.

Now for the joint-caulking!
DAP has some good paintable caulks, but ask at your stores, Dynaflex 230 is a great all-around caulk; Polyseamseal is too; and, inquire about their "painters-caulks" too.
* Big-Stretch brand caulking is good too, IF you have unusually frequent movement.
* Paintover times vary here...read the tubes.

ONE TIP: Cut a SMALL opening, 1/8", and PUSH the gun away from you when applying. This motion gets the caulk into cracks better, instead of "barely sitting on top".
* Then, use a wet finger, damp sponge, or other tool, to smooth off your bead.

>>> Some painters prime b4 this caulking-step, some after. I'll completely defer to them!!!

>>> For filling outside corner wood-mitre's, use a wood filler that hardens, and can be sanded/primed/painted. Caulk is OK for inside-corners.

FINALLY...
You've got beautifully cleaned, de-flaked, sanded, smooth, primed, & caulked (whew!) trim THAT WILL HOLD & DISPLAY YOUR TWO TOPCOATS OF PAINT BEAUTIFULLY!!

(after all this...don't skimp on the Finish-paint OR the brushes!!!)
Option- try adding some of XIM's Latex Xtender for more open-time when painting. It helps leveling too.

Faron

Thank you, Faron!

Any thoughts on how to get a crisp caulk line? Should I use tape? I can paint without tape but caulk is not my forte!