Nobody can predict every single one of the changes children would have to deal with when two families decide to combine into one. When two parents with kids of their own decide to marry and share the responsibility, it's quite impossible to know in advance what struggles they will have to deal with as they raise their respective children together.
Some changes can be easily expected-the struggles of moving into a bigger home and figuring out bedroom situations, jealousy and competitiveness between the two sets of kids, and the resentment that may be felt and expressed. Other changes reveal themselves as you go. Like how difficult it may be to live as one family under one roof when one family's financial situation has been drastically different from the other's up until now. Or how each parent has rules and educational standpoints that are vastly different from the other parent's, and now have to be morphed into one.
It seems as if the couple in the story below did not expect the struggles that their financial differences might lead to, and it seriously complicated the family dynamic.