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There is absolutely nothing wrong, growing three small plants in a single pot. You just want to be sure the pot is adequate size to afford their growth for a year or two and be very careful to use very well draining soil and plenty of drain holes in the pot so that the potting soil never gets soggy.
Now, that's the easy part, the first couple of years. There will come a time that these cute, little, fat-caudex, plants will get large. They'll begin to crowd each other in that pot. You could increase the size of the pot, but still, this would have to be done every few years. At some point, just so that the pot isn't getting huge, you'll want to separate these plants, each having their own pot. Desert Rose (Adenium) plants do best in full sun and they won't take cold or frost.
Here's an example of what you might expect, given enough DECADES of growing.
Those two pots you see are 26" in diameter and the caudices of these two plants fill those pots.