I'm writing a story about a little girl who got bit by an unknown snake species and is being treated for it. Out of the 3 snakebite victims, this little girl seems to have the best prognosis. Here is a summary of what happens in the second chapter of my story, where I introduce a foreign language speaking character.
Peter, the little girl's brother is at school and tells his dad about the situation during a break from his classes. He shows a picture of the snake. His dad, an expert herpetologist goes to the park where the snake was found and sets a lot of snake traps. Peter hears the news the next morning about his dad setting the snake traps. On the news is some live footage of his youngest sister, Lily and her mom, Paula at the hospital.
He feels too sad and worried to just stay home with his older sister Alexandra, so they decide to go to Grandma's and tell her about the situation. Grandma greets the two of them in Spanish, her native tongue. Peter knows enough Spanish to communicate to Grandma about the snakebite situation but is clearly not fluent in Spanish.
Grandma drives them to the hospital and offers Lily some orange juice. Paula declines the offer, despite Grandma's justification that it will help her immune system fight off the snake venom. Grandma doesn't know it yet, but Lily is blind. Paula says that Lily needs her rest and is worried that she isn't ready to eat or drink anything since she got out of a gravely dangerous situation of not being able to breathe.
Grandma in my story speaks Spanish as a native language, Paula is bilingual in Spanish and English, Peter is actively learning Spanish, Alexandra and Bob, Peter's dad, both understand some Spanish but aren't actively learning it, and Lily can't understand Spanish at all yet.
So there are several ways that I can think of getting across foreign language in the dialogue. First off, there is writing the foreign language directly. However, I am not a native Spanish speaker or even conservationally fluent in Spanish. Also, given that I live in the USA, I don't know how many people will understand it if I write the foreign language directly. Then there is writing completely in English and just mentioning that it is spoken in Spanish. Then there is writing a romanization, in other words writing it the way that it is pronounced instead of writing it the way it is spelt.
What are the advantages and disadvantages of each of these 3 ways of getting across foreign language in my dialogue?