Assembly wasnt hard, could be done by one person if you are able to lift about 50 lbs. Unfortunately, parts very poorly fitted, especially between the bed frame and the shelf-staircase, they could not be join together tightly and completely with the provided bolts and screws. This is my first concern as the kids are very likely to jump up and down on it, accident may be easily caused if the parts are not stable and fixed enough.
I may not return or request for replacement, but in case of lowering risk, I will avoid from buying products from the same sellerbrand in the future with all my efforts.