I inherited a struggling peace lily at work and it ended up getting quite big and splitting multiple times in a self watering Ikea planter. It starting looking really big for the planter and was root bound(big rectangle root mass in the bottom of the planter).

Decided to split and repot two weeks ago, now 4 plants are doing ok, but 3 are in poor shape. I used the same miracle grow moisture control potting mix I had used in the Ikea planter.

Tried to repot again in perforated styrofoam cups, which I did to successfully repot a small offshoot previously.

It's a new feeling to me, but this plant is on my mind constantly like a sick child! Any help would be greatly appreciated.

Images of the ok repots compared to the struggling triplets can be seen below.