Leaving Islam/ telling my family I'm athiest?

I have looked into it enough and it is anything but logical to me and most others.

May Allah guide you and soften your heart

Read the 'or' afterwards, it might make it easier to understand why your post is still irrelevant...

Because you claim that atheism leads to destruction in their life - yet societies such as Sweden are majority atheist but are the opposite of destroyed. So you're wrong.

Curious, isn't is, that "kaffir" countries are on the whole so much more developed and have a higher quality of life than the countries where God's supposedly chosen people live.

This has been very much the case throughout History and it always fluctuates.
i.e. The Islamic world is dominant at one point then its the 'kaffir' world, then it's the Islamic world and then it's the Kaffir world again.
This has happened through tout History and only Allah knows the wisdom of this.

Curious, isn't it, that "kaffir" countries are on the whole so much more developed and have a higher quality of life than the countries where God's supposedly chosen people live.

"...they were arrogant in the land without right, and they said: Who is mightier than us in power? Could they not see that Allah Who created them, He was mightier than them in power? And they denied Our revelations."

Circular reasoning, denying these so-called revelations has not led their countries to destruction, if anything the opposite.

No True Reason Falacy

There's no such fallacy

Philosophically ponder and you will realise that science will never realistically explain where the Universe came from, even from (unsatisfactory) theories, and God is probable to exist; arrogant New Atheists feel that people use God as a miracle answer to the question of the universe, however it is the most logical answer, and based upon this, as much as it displeases many, religion actually makes sense and provides moral, social, psychological and spiritual order in people and society much to its benefit. Many theists are too lazy to question their belief (to later affirm it), and many atheists are too lazy and too arrogant in their 'intellectual' superiority and belief of self-suffiency to consider that a God exists and sustains everything...
Having almost been atheist once, I understand how 'liberating' and 'logical' it feels; upon reflection it is just the lazy man's way of ignoring the question of fundemental origin.

Perhaps one day you will realise that your family are not just sheep in flock following the crowd, and realise that the liberal YOLO atheists are exactly what they accuse the religiously minded of being...

Now your point is completely unfalsifiable. You're giving a possible explanations for what will happen, and then claiming victory when one or neither of them happens. Do you see how that is a problem for your view?

The Islamic world had one golden age, I'm not aware of it becoming more advanced than the "kaffir" countries since then. And ah, the good old "Allah knows best" card when the questions get tricky.

There is nothing tricky here, there are good explanations you can find if you search.

There wasn't only one time Islam was dominant, there was intially with the collapse of the persian and byzantine empire, there was the golden age (andalus /spain) and there were the ottamans.

Not really, there are plenty of issues for which there is no satisfactory answer. Perhaps you'd like to explain why kaffir countries seem to be so successful while muslim ones are mostly dumps?

The Ottomans were not more advanced than the western world, their empire wasn't even the biggest or richest at the time.

And the muslims in Spain were finally defeated by the Christians. Why did Allah allow the kuffar to beat them?