First off-- as some sage person advised me once-- no matter how awful the flight, it will be over sometime! And you will forget it. Eventually. ;-)
We have flown Malaysia (KL-AMS) several times with 2 kids and they are really really child friendly. I suspect the crew will do as much as they can to accommodate you, whatever the official line is... I would still advise getting a seat for the baby if you can afford it-- 12+ hours is a long time, you will probably appreciate being able to let baby sit somewhere when awake (IME, a car seat was better for my daughter to sleep in than a bassinet, so getting the bulkhead became less of an issue. Depends on the baby... But I wouldn't plan on being able to move it around a lot during flight.)
Couldn't your husband (with the toddlers) sit across the aisle in the 3 configuration? Also, you may also be able to put the child seat in the middle of the middle aisle (bulkhead)-- the idea is that it shouldn't block anyone else's exit.
Oh, and every MH flight we've done has had those personal seatback entertainment stations-- I'm not big on TV, but in the middle of the nihgt it was a great help with the squirrely toddler.
Just our experience... FWIW, I found after doing 36+ hours Asia to the US, no shorter flight can faze me anymore ;-)
Good luck!
K.