Mistakes in the ml, borrowing from the ML

Back when we had decided I would speak English to our children (our ml), hubby offered to do the same. His English was non-existent before we met. He's learned English by watching TV in English and travelling. He now understands almost everything, his vocabulary is pretty good, but his grammar is very poor. We had to choose between quality, which we were lacking anyway, and quantity (2 parents vs. 1 speaking the ml). We went with quantity, and I think we made the right choice, as our children seem to feel more comfortable speaking in the ml so far.

The problem is that my daughter is learning lots of mistakes from her dad that are hard to correct later. My husband has corrected some, but she's still using them: "for+to" ("This is for to walk"), "put" instead of "put on" for clothes ("I put my pants"). The one that's driving me crazy lately is questions. She'll say things like: "how I can do this?" I thought it was something she said, but then I caught hubby saying something similar. Today, she told me that she can now do something because grandpa learned her.

I feel that I'm always correcting what she says, many times a day, but don't know what else to do. I usually rephrase what she said, like "oh, grandpa taught you how to...", putting emphasis on the word she said wrong. I pretty much feel like I am, as Amy calls it, the language police.

I'm okay with mistakes that I find normal in a bilingual 4yo, like "she doos", instead of "does", or "she want", or "you didn't be", even "a orange". She's regularizing irregular verbs, not getting that the 3rd person singular needs an extra S, or missing that "an" is used when followed by a vowel sound. But borrowing from Spanish (ML) or not getting basic grammar rules, like how to ask a question, bothers me more. Anyone else having this problem? Any ideas on how to handle it?