Heythere!

"Coincidentally, one of the three died in each pot." Hopefully we can help you improve the conditions for these plants so they grow well, not die. This statement puts a shadow on everything below because I am worried that your plants are not healthy enough for propagation, or getting enough light to recover easily from the kind of root trimming they likely need. So please read the rest knowing that it's intended for a healthy, vigorous plant. Yours may be perfectly healthy, but knowing that part of it has perished, (which I'm not sure is a section of a still-growing entity, or a single trunk from a multi-trunk pot,) it's concerning and I would want to know what kind of condition your specific plants are in before doing or recommending anything for those particular plants.

"I understand these guys have limited roots, so pulls them apart wouldn't hurt them right?"
I think you'll find the pot is mostly full of roots. If you are planning to combine them, I'm not sure why you would want to pull them apart? Cutting apart would probably be better if actual untangling is not possible.

"Since the roots system is small, they don't need a lot of dirt, do they?" The root mass after it's had the old soil removed, and the roots trimmed, may be surprisingly small, but if given a large pot of a decent mix, the roots will soon fill it.

"I can cut away some stems and they will all grow back, wouldn't they?"
This depends a lot on how healthy the plants are. If they have the energy reserves, and the proper conditions, you should get new tops. There are no guarantees. You might get {{gwi:114423}}. (Not my excellent pic.)

"I was told that the green stems with leaves can be rooted and grow as stalk-less cornplants? If the stem is 2-3ft tal l with lots of leaves, how to root them?" Just stick them in a pot. Below is one I took from a large plant. It's normal for some leaves to be lost in this kind of operation. I'm letting the plant decide which of these leaves it wants to eliminate, and use whatever reserves they have until they turn brown. It's been 2 months and the top is green and growing, so it's reasonable to assume roots have formed. If there is a length of healthy stem you don't want on either old or newly propagated plant, it's possible for those to be propagated also (which I believe is the rest of the story of what is pictured in the "two" link above.) If you're interested and were going to discard anyway, takes about 2 seconds to literally stick it in the pot. Just make sure you keep track of which end is which, it must be in the same direction (with the end that was closest to the roots being the end that is stuck in soil.)

If you are able to show picture(s), the advice would be more specific. Before getting into taking your plants out of their pots or cutting off pieces of them, (in addition to verifying...

Hey Purpleinopp. thanks for helping, of the two pots:

Pot 1.
Dead stalk was about 3-4 years when it wasn't taken care of as it deserves. I have cut the dead stalk at dirt level when it was totally dried and puffy. It flowered about 2 years ago. When it wasn't taken care of, it lost lots of leaves, so the all current leaves are towards the top. I am hoping that once the stems are removed, the new growth will fill up the empty space.

it's currently 8.5 ft tall in a 10ft ceiling room.

Pot 2
Similarly to pot 1 but shorter at less than 8ft. The two tallest stems are weak, being supported by stalks otherwise they will wilt and tilt.

For both pots, the original nursery planted all the stalks too close like 3"-4". I would like to use a bigger pot (24") and plant them like 8"-10" apart.

make sense?

"It flowered about 2 years ago." That's really cool and fairly unusual!

"When it wasn't taken care of, it lost lots of leaves, so the all current leaves are towards the top. I am hoping that once the stems are removed, the new growth will fill up the empty space." If by filling the empty space you mean growing new tops, then yes, that's likely. Unfortunately naked trunk/stem area will not grow new individual leaves.

"it's currently 8.5 ft tall in a 10ft ceiling room." Wow! This is a seriously large plant.

"The two tallest stems are weak, being supported by stalks otherwise they will wilt and tilt." It's hard to say if this is from being inside without any wind to fight against, which causes trunks to strengthen in response, or if it is from a health issue.

"For both pots, the original nursery planted all the stalks too close like 3"-4"." The large roots coming from each may be so tangled that they need a saw or pruner to cut and separate. At 3" apart, that's likely to leave some roots at 1.5", pretty short. If the root mass left on each plant is still sufficient after separation, both plants should continue to live where you put them. Kind of a difficult situation because you've got to dig and cut into it to find the answer. The link above shows the roots of 2 trunks planted as close together as you describe. Separating these plants would absolutely have taken a saw. They were too solid to get in there with a pruner. Putting both individual plants into one giant pot sounds like a fine idea, but separating the individual trunks that have been growing together for so long, I would regard as quite risky.

"I would like to use a bigger pot (24") and plant them like 8"-10" apart." I don't feel like there's enough info here, especially without any pics, to answer this.