I have a Mexican Citizen father and four Mexican-born grandparents. I'm a first and second generation American and my first language is Spanish. My husband is English and my kids are dual. Our household uses English-American-Mexican words all the time. About two minutes ago, I just told my son to: "Por favor, niño, go upstairs and collect the trash from all the bins and put it all in the garage (the English way) porque mañana vienen the trash men y temprano".
I don't really notice the words I use until someone points it out. My sister has to ask me what certain words mean so I'm using an English word or expression. Other days, I can't find the right word in the entire English language to mean what I want so I'll just say a random Spanish word and strangely, my husband sort of "gets it". If I'm speaking to my in-laws over the phone, I'll have to use English words but it does sound a little strange. I say "petrol" but I also say "gas" or "gasolina". My son, after 12 years in the US (he's 19) still has an English accent and when he uses American words, it sounds strange. My daughter is 15 cannot fathom ever using an English word because she says it sounds stupid to her ears. So, I'm willing to guess it's a preference.