Availability of using 2 pole circuit breaker instead of 4 pole circuit breaker
No you cannot. It's a requirement that if a breaker senses an overload or short circuit, that it open ALL poles, so multi-pole breakers are made with what is called a "common trip", meaning all poles open at the same time. By using 2 x 2-pole breakers, you could have a situation where only one of them trips, leaving the other energized. that is extremely dangerous.

And for those in North America who may be reading this, there are some systems elsewhere in the world where the Neutral must go through a breaker, hence a 4 pole breaker (we don't do that here).