This is interesting. It makes sense that the more people in a family, the harder to fit them in one ceremony. I mean they have to move four single applicants for your family, even though they might have applied around the same time or later than you. Way easier to deal with one complaint than four
Also the call centre agents sometimes don't have (or don't wanna give) accurate and detailed info (more work for them). I used to work in customer support so I know this
I even suspect they sometimes make up things just to make you go away, which is why I never wanted to call them. It could be one of your family members has certain issue (most likely minor, as they don't make big lies, only small ones that are close to the truth) that's dragging but won't change the outcome, so they simply tell you everything is fine
Either way everything should/will be fine so don't worry.