“While yet others” is perfectly fine. Employing while as a coordinating rather than subordinating conjunction is a natural and widespread extension to which only the most reactionary of pedants would take exception. But in your construction it should not be followed by a comma, because “others” here is the subject of the sentence which follows:
While yet others have decided ...
If you want to maintain strict parallelism, you should start your third sentence with an “In” phrase as well:
In certain countries, the debate ...
In others, ...
In yet others, it has been decided to ... (or something similar)
But this is a rhetorical nicety which is not obligatory, and in fact will not even be noticed unless your sentences are fairly short. If your sentences are long, or if more than a sentence intervenes, you would do better to mark your periods with a repetition of “countries” as well, to make sure your readers keep their bearings:
In certain countries, the debate ...
In other countries, ...
In yet other countries, it has been decided to ...