Singularity at the time of origins According to the big Bang Theory, the universe have started from a point and it describes how the universe expanded from a very high-density and high-temperature state.The initial singularity was a singularity of infinite density thought to have contained all of the mass and space-time of the Universe. If it was so dense,  why didn't it engulf the other parallel universes just like a supermassive black hole? 

If there are no other universes,  why the existing black holes didn't suck the entire universe yet?
First thing to mention is all our limited knowledge (best guesses) from back than only goes back to the fraction of time just after the big bang not the creation moment itself. Moreover you have to remember that spacetime itself was also created at that moment as well as all the stuff in it. This means that using the term singularity as we understand from the core of a blackhole, which is to say an infinitely dense and infinitely small point/puncture IN the fabric of space doesn't really marry up. The universe no matter how tightly packed conditions were at this early stage had no space to warp/puncture into.

The universe has no centre, it began everywhere, simultaneously and instantly with all matter distributed uniformly and in equal density. Without a central point all matter was pulling evenly on its self in all directions so wouldn't coalesce at a single point and collapse down as it does in a black hole.

And as to your mention of supermassive black holes sucking in parallel universes "they don't"

Hope this helps