Sadly not. You do have to go through all levels in order.
That being said, I am in a similar situation, but I really like their system, so I don’t mind too much going through stuff I already know.
You have three levels to get a better idea. If you are still on the fence after that, I can also tell you that I started enjoying WK way more from level 5, so you may consider trying a one month subscription as well.
WK does not teach grammar. I guess you could figure some stuff out from reading the example sentences, but I wouldn’t rely on it. In any case you will have to find other resources for that.
Anyway, good luck!