"my BIL is German and his English grammar is faultless"
Well, compared with German grammar ours is so easy! For instance, they have 16 different ways of saying 'the'. (four cases, three genders = 12, plus 4 cases in the plural, which is the same in all genders, =16)
Oh, and to make things even more complicated, their three genders are largely random. Why is a table masculine, a door feminine, and a window neuter? Some words have a specific ending which tells you the gender, but there are not enough of them.
They have their arguments about grammar too. For instance, the word/acronym 'Modem' is neuter if you think of it as a foreign word, but if you think of it as a phrase ending in 'Modulator' it is, I think, masculine.
We have it so easy, but still so many of us get it wrong. Why oh why?