well, to my shock the Reina Sofia customer service email replied-
so here is their response:
Good morning,
There are no guided tours of Guernica work.
All the free tickets (for under 18 years old, senior (65 years old or older), people with disability, unemployed, students up to 25 years old foreign students are recommended to present the international student card, ISIC, teachers (foreign teachers are recommended to present the international teacher card ITIC), Youth Card holders, large family’s group, ICOM, Mutua Madrileña’s card holders, etc.) cannot be booked in advance.
These tickets must be collected directly at the ticket office and only if there’s availability. Therefore, we recommend checking the availability on our website before going to the museum.
Accreditations in languages that do not use the Latin spelling will not be valid. The corresponding international accreditation or a certified translation will be requested.
Large families: Family group composed of at least one adult and three descendants (or two, if one of them has a disability) included in the same family title.
A person with a disability who brings a companion with him/her may access free of charge as long as the companion is essential for the visit and this circumstance is stated in the disability card or resolution issued for this purpose.
People who have purchased tickets online and are accompanied by people who need free admission, can go directly to the express ticket office, show the ticket purchased online and they will be given free admission for people with free admission.
Reduced admission 50% with accreditation (only at ticket offices):
Cultural volunteers, members of large families, museum staff not attached to the Ministry of Culture and Sports.
Please note that it must be accredited with the accrediting document valid in each case, and duly updated, which visibly reflects the period of validity or expiration date.