When did your trilingual+ kids catch up with monolingual peers?

I have twins who will be 5 in April, and they're exposed to 4 languages. We do OPOL (French with my partner, English with me) at home, but I only work part-time and have the afternoons with them so they hear more English than French, about 70/30. They go to a Catalan-language school but almost all the kids speak Spanish together and some of the staff do too. Activities and events they go to are almost always in Spanish. We also spend 2-3 months of the year in Scotland with my family, where the environment is pretty much 100% English.

At the moment, their English vocabulary is excellent but their grammar seems to be way below the level of a typical monolingual 4- or 5-year-old. They mix up tenses and often just use the present. One also uses the Spanish "se" in English constantly, eg "se do it like this", "no se hit". I repeat what they say in the correct form as much as I can, and lately I've tried to tell them "we don't say that in English, we say X" sometimes but I haven't seen much difference so far. We read a lot, which I think has improved their vocab but they don't seem to be picking up the grammar from it. Is this normal for their age and language exposure? Or do I need to be doing something else?

Their Spanish is similarly mixed, great vocab with limited grammar, but their teacher says they express themselves well and she's not worried about it at this stage. As for French and Catalan, they understand everything but don't speak much yet. I'm mostly focused on their English and Spanish at the moment so we'll think about those later!