He loves and respects his mother, but they spend a lot of time arguing. I don't think there'd be much formality between them, but at the same time, I wouldn't say there's disrespect either. What might he call her?
He has two younger sisters. Is it normal in Spanish to just call siblings by their names, or something else?
The youngest sister, I'm thinking he probably has a nickname for, something along the lines of "runt" or "squirt" or whatever other teasingly affectionate type thing a big brother might call a little sister. But, uh, in Spanish. Help?