clrose, after visiting this site quite some time ago, I ended up moving my cats over to a canned food only diet. My cats didn't have the trouble yours did because they had been 1/2 canned and 1/2 dry before, but the switch made a big difference.
My two overweight cats both lost a couple of pounds (one is still overweight though).
Hairballs decreased by about 75%.
I mean HUGE. My three longhairs who are responsible for the vast majority of them were puking up multiple hairballs a day. Now, even during the spring and fall, I'm not even sure they throw up one a day!
One of my boys, who was getting UTIs every few months, hasn't had one in eight months.
It might take them a while to get used to it. In the meantime, the canned pumpkin might very well help settle their stomachs.
Storm (beeps and has a pink nose and toes),
Misty (with big blue eyes and tasseled ears),
Anya (only ever called Honey - she's that sweet),
Zander (who goes by Punkin' cause he's almost that bright)
Kasee (couch potato who thinks she's a dog)