Note the distinction between a sextuplet (an irregular grouping of six notes) and the corresponding pair of triplets. At least conceptually these are two different things. But if you could actually hear a difference from a performance is another matter (what you could do is to make small accents on the first, third and fifth notes in the sextuplet and thereby stress a grouping of 3x2 notes instead of 2x3).
Note also that modern music notation software usually are very flexible and that some tuplets that are possible to produce may be more or less confusion to read or perform.
In your three examples the first is unproblematic; the second is confusing, because it looks like a sextuplet but you have a '3' instead of a '6'; the same is also true for the third example (but here you have made clear that the grouping should equal to a pair of triplets).