Hey, I was wondering what the correct way to group notes in 6/4

I have a dotted minim - minim - crotchet rest

is that 'gramatically correct'?

Yes, I think that sounds ok.

Think of two dotted minim beats.

With compound time, it's mainly necessary to remember the rests. If your notes were slightly different, with a dotted minim note at the start of the bar and a crotchet note at the end, you could have one minim rest in between them. If there was a dotted minim note at the start, followed by a crotchet note after it, you would need two crotchet rests at the end of the bar and not one minim rest. Theory is fun.