Really the only way to guarantee a stateroom upgrade is to book it and pay for it.
There seems to be no rhyme or reason for DCLs upgrades.
I wouldn't worry too much. Any room when your with your family for special occasions will be great.
We just purchased cheap inside cabins (unfortunately on RCL) for my In-Laws 40th anniversary. They're thrilled to be going on a cruise. Extra special since they'll have their kids and grandkids.