It also depends on the languages you already speak.
Swedish/Norwegian/Danish do not really have "little grammar", but for an English speaker, there probably won't be any need to explicitly learn the grammar, since it works mostly like English. But on the flipside, they are just as difficult as English for speakers of unrelated languages.
>for an English speaker, there probably won't be any need to explicitly learn the grammar, since it works mostly like English //
For a period in the UK there was no English grammar taught in schools. This caused me great problems in Russian class (second high school language) as I had no idea there were cases in English and so had no reference for why a case was needed and what it did. The entirety of my English grammar training was learning a poem by rote for homework, which I didn't do ("A nouns the name of anything [...]"). I learnt the little grammar I know from French lessons. So, YMMV depending on the English speaker.
Having left school 3 years ago, I can confirm there is still no grammar taught in english lessons. It was all taught to the AQA exam we did. I studied french and german too, and all my grammar knowledge comes from there and from languages at uni. There's obviously basic things in primary school but that's like where to put commas, that's it.
Historically we were taught Latin grammer disguised as English grammer - so 'tenses' when English only has two tenses (past and present) and 6 or more moods (shall, could, will, might etc, etc)
Most English 'grammer' discussed in the Anglophone world (split infinitives WTF? English doesn't have infinitives) is gibberish...
Well, now they teach made up nonsense about "fronted adverbials" ("Stupidly, they do it too early.") in primary school, they spend quite a bit of time on sentence structure and labelling the parts of speech. It's too much IMO and comes easy too early.
So verb forms are not the only part of grammar. In these examples you've covered sequences of tenses, mood, word order, and it could be argued aspect. Ask someone to point out the parts of speech and they'd be able to point out the pronoun and verb, that's usually it.
Swedish/Norwegian/Danish do not really have "little grammar", but for an English speaker, there probably won't be any need to explicitly learn the grammar, since it works mostly like English. But on the flipside, they are just as difficult as English for speakers of unrelated languages.