How is Sociology possible without Psychology?!?

It's been said that the mind came to existence for our survival. The reason we may a have a mind is to facilitate the proper investment/expenditure of energy. The logic behind this is kind of simple; we have a mind so our behavior doesn't go to waste. We have a mind so that the pay off for our behavior is worth the work we put in. We can't survive if we waste more energy than we consume. The mind is definitely a relevant thing to take into consideration when studying things like how people behave in groups (i.e., sociology). I think you might benefit from doing some research on "behavioral investment theory".

Sociology began precisely when scholars, namely Durkheim, realized that society is something more than just a collection of individuals. There is no sum of minds that will become a society.

And even if that weren't true, the idea that one scientific discipline can be reduced into another because the second one is the 'real' cause is called reductionism in philosophy of science. Scholars like Edgar Morin have explained how knowledge is simplified by means of reducing biology to physics, and sociology to biology. Reducing society's complexity to the brain's complexity is still a form of reductionism, a simplification of the complex.

Sociology and Social Psychology are very closely linked by many studies.

It's a good question.... Sociology seeks to study human "systems"...How humans interact with each other, how societies work, how we organize... Etc. But all these things are conditioned by the human condition....Our hard-wired characteristics and responses and instincts. Despite 10,000 years of civiliation, we are still the same guys that drew those paintings on the cave walls...

So the way our brains work must be taken into account for any meaningful study of how we interact with each other, either individually or societally.