Dumbo is recessive so neither parent has to be dumbo, but both have to at least carry the gene.
I'm not seeing any dumbo ears though, every ear shown is a top eared ratty.
Still cute, hold back a male and a female or 1.2 and breed them to see which gene they carry.
The mom obviously didn't carry blue or Siamese, whichever was the sire, but the babbies will be all het blue or het Siamese