1.
La lluvia arreciaba mientras volvían a la oficina. can be translated as
Rain intensified while they were on their way to the office
you can't use "en cuanto" to express the same situation , since it expresses a completed action, example
en cuanto llegaron a la oficina , la lluvia arrecio.
as soon as they arrived to the office, rain intensified
2. Mientras Pedro estuvo al lado de su esposa en el hospital, no fue nadie más a ver a la enferma
While Pedro was beside his wife in the hospital, no one else went to see the patient(the wife).
you cant "A medida que" because it gives the sense of a progression, like something is going to happen over and over again, examples:
A medida que surjan imprevistos modificaremos el plan original.
Whenever unforeseen events occur, we will modify the original plan.
A medida que creces cambian tus gustos.
Your tastes change as you grow.
and about the meaning, well, you cant tell the reason why... since there is no context but.. I wouldn't think that Pedro is a scary person , I would think that, everyone else was busy and couldn't make it to the hospital , or as you say, she has no friends, or maybe they were on vacations far away from home so there was no one near, otherwise it doesn't seem like a plausible situation
hope it helps :)
Saludos