Instead of looking for ways to ereduce their tax rate, as is written in a Le Monde article about the 25 richest Americans who are only paying 13.6 Billion dollars of tax while their common fortunes grew by about 401 Billion dollars whereas millions of Americans pay more tax than the 25 richest although they have less money.

Which onsentence is better and c? Corrections please!

I think it works better to split this into two sentences, since it is two separate thoughts. Also, to replace "one" with the more specific "sentence". Perhaps this is my option, but I think it reads better.

Millions of Americans are actually paying more tax tha,n the 25 richest Americans.

This sentence reads a little strangely to me. It seems like "Americans" should be made more specific. Maybe you could write millions of Americans 'closer to the average income mark'?

In fact the latter are paying $13.6 Bbillion even tough their combined fortunes grew by $401 Bbillion.

No need to capitalise billion.

Instead of looking for ways to erduce their tax rate, as is written in aA Le Monde article aboutconcerning the 25 richest Americans who are only paying 13.6 Billion dollars of tax while their common fortunes grew by aboutrevealed that their common fortunes had recently grown by roughly 401 Bbillion dollars whereas m. However, these wealthy individuals had paid only 13.6 billion dollars of tax. Millions of Americans paid significantly more tax than the 25 richest although they havese ultra wealthy individuals - despite having far less money.

I found the original sentence a little too long and so have split it up. It is more readable now because it does not run on with too much information separated by connective words such as "while," "whereas," and "although".

Which one is better and c? Corrections please.

Millions of Americans are actually paying more tax tha,n the 25 richest Americans.

Not needed, however, the sentence feels like ‘Americans’ needs to be clarified.
E.g. Millions of average income Americans.
Or
Millions of tax paying Americans.

In fact, the latter are paying $13.6 Bbillion even though their combined fortunes grew by $401 Bbillion.

Billion, million etc (unless at the start of a sentence) are not capitalised because they follow the possessions class rules.

How come?

Correct sentence for informal use.
Formal use would be something like “Why is this?”

They are using many ways to reduce their tax rate ¶
.¶
¶
2.

Instead of looking for ways to ereduce their tax rate, as is written in a Le Monde article about the 25 richest Americans who are only paying 13.6 Bbillion dollars of tax while their common fortunes grew by about 401 Bbillion dollars whereas millions of Americans pay more tax than the 25 richest although they have less money

A Le Monde article about the 25 richest Americans who are only paying 13.6 billion dollars of tax, while their common fortunes grew by about 401 billion dollars, states, millions of (average income?) Americans pay more tax than these 25 even though they have less money.

Instead of looking for ways to reduce their (’their’ needs clarified e.g. millions of Americans/25 richest) tax rate, …. (Sentence needs completed).

I’ve re-written this section because the sentence was too long and it read very clumsily. I was struggling to work with the structure you wrote. This way it reads better.