It is normal that to the visit they give an official character because the hosts are the Chief of the German State and his wife.
Duke, the only disease to which the Queen Sofia is related is with the Alzheimer, because from her foundation she has a project destined to investigate it and treat it.
If you revise the acts of the Princess you see as the organizations of the cancer, the autism and the rare diseases, appear in several occasions.
About the Infanta Elena, it is true that the past week she presided the day of the Rare Diseases, but I believe that it was something circumstantial. The Royal Household needed to give her an act because she had passed two months without going to an official act and with the advertisement of the divorce she was a news.