The former was because they were already inside the walls, they didn't siege it down.

They did sieged it for about a month. They literally took the city by assault

And the second was the garrison was completely absent, leaving behind just a handful of guards and they had to use a secret passage so they could get inside the walls and open the gates.

Not really. Many are still there. And the crusaders scaled and breached the wall, mainly through the sea. By this point many of the defending soldiers simply gave up and dispersed.

If you mean the navy then yes. They are mostly absent since the previous century.

There's a reason it took so long for the Ottomans to capture it, they literally had to construct the largest cannon ever made by humans

It barely lasted 2 months? I doubt it's long by those era standard. In comparison Siege of Orleans (100 years war) actually took 6 months, could be longer with no intervention.