Do you know when it was repotted last time?

The plant is doing well. Repotting could do it more harm than good. My approach is, if plants are doing well care for them as usual (the same way as your grandmother did), otherwise leave them alone.

The plant is somewhat thirsty, indicated by some of the segments looking wrinkled as the OP observed.

I wish Josh (Greenman) were here to counsel on handling such a large & old plant. The thickness of the base stems confirm it's very old. I think it's a crap shoot either way.

I think Mamapolina's instincts are correct abt the gaps in the soil being potential trouble. When the soil is dry, does it become hard to your touch?

I'd pick out all the dead growth & take a skewer, insert into the mix all the way down to the bottom at intervals near the wrinkled leaves & then water directly into those holes. That will ensure that the water gets down deeply into the rootball.

I agree with windberry. Leave the plant alone. Looks like you picked a nice location for it. If you start messing with it, you’ll be sorry. Grandma left you a nice plant. Janice

Could be too much direct sunlight if the windows are facing S or W, How much sun it was getting when at your grandma?

It's not too much direct sunlight; that usually causes a color change in the leaves (segments). Makes them slightly reddish or purplish; it's not especially harmful to the plants, I've had it happen to some of mine yrs. ago.

It's just not how they grow in nature, tending to get dappled light, bright, but indirect as they naturally grow in the crotches of tree branches, not in the ground in soil.

Light would be problem only if it was kept in very low light before op received the plant. But even then, it is in the corner that cuts down on light. Light coming thru the window panes is much less intense too, and even more so if windows have any UV protection (we don't know that). I also see another plant that seems to be in front of CC. So light doesn't seem to be the problem. Karen is correct. I have large TC (not CC, but they have similar needs), that I keep outside, and it gets quite a bit of sunlight. Color of segments gets reddish, but they do not shrivell.

As you can see, segments are not wrinkly in much stronger sunlight than op's plant This plant was given to me in 2012, and every spring it goes outdoors. I am not suggesting to do same, just pointing out what happens to segments i lots of sunlight.

I have few TC, 3 young CC and few Spring/Easter cacti. They all seems to react same way: if thirsty, leaves get droopy and may shrivell. I try not to get them to that point...

mamapollina

I actually do not see wrinkled segments. Is it possible for you to take close-up, clear photo of the problem?

Look at the 2nd pic pls RIna, it's only visible around the 6 o'clock position, then slightly left & right of that. Really just in the bottom 1/3 of the pix or so, somewhat subtle.

Yours looks like a large plant, I see it's subtly purplish, but nice since it's uniformly all over purplish. Curious, is that the TC, as its joints look pretty rounded (ish) ;>)

Karen

It is quite large, but smaller than CC mamapollina has; stems are getting woody too. Judging by the blooms, it is TC - even if the segments look more CC-like. Blooms are asymmetrical and grow horizontally (CC blooms are symmetrical, and extend downward. Pollen is yellow.). They are red, pink, white or yellow
(maybe some other colors?):

Josh and few others suggested it could be some hybrid of CC.

I am not absolutely sure, but CC blooms are red, white and occasionally yellow, but not pink. Pollen is more brownish. Here is the bloom of my CC plant:

Interesting Rina, I'd wonder abt it being a hybrid too, I can believe Josh might be the guy that knows.

What I've usually heard & read is the traditional, heirloom CCs bloom pink; the ones that are handed down & can't be bought bloom pink; it's what I've always heard.

I've been given a few different pieces from several diff. people, over the last several yrs. but none have bloomed for me yet.

Maybe I'll get lucky w/ them this Winter, especially the one I grow in Hydro which I discovered they LOVE!

Pls go over to Houseplant Forum & look at my thread called 'Finally Thriving Christmas Cactus'. Seems when I posted it, instead of posting at C&S, I must have mis-hit the keys, as it appeared at Houseplants, C&S Exchange & Plant Propagation. Only just discovered that -- oops.

Sorry to digress your thread Mamapollina.

It is S. X bucklyi.

Which pls Rob? The OP's or Rinas?

Mamapolina's for sure, Rina's I guess it is too. X bucklyi has red and white flowers and soft leaves, no horns.

Rob

If you think that my large plant (pink blooms) is Christmas cactus, how about ID by flowers and pollen? And they are pink, not red.

Rob, my CC plant from the cuttings you sent me has been growing like crazy this summer. I treasure this one :-)

(sorry all for the slight highjack here)