Is it right to say like this sentence?
Less babies as they are having, there still increases the population.
I mean
Although they're having less babies, the population still increases.
The first sentence is not correct.
Ignoring the first part, and stripping the adverb "still," the main clause
There increases the population.
Is not an idiomatic way of saying
The population increases.
There are only a few verbs in English which allow rephrasing to make "There" the first word of the sentence, and "to increase" is not one of them. Usually these verbs have to do with "existence, coming in to view, or being in a specific location" as @Araucaria says in this ELU answer, which you can read for more information.
Finally, as "babies" is countable, "fewer" is preferred in place of less, and a continuous form for the verb "increase" would be more natural for a process that is ongoing.
Although they're having fewer babies, the population is still increasing.