Very sorry for bad photo quality, but I hope the notes are visible. Here, have I done anything wrong with the grouping?!
The second measure is fine, but the first one is wrong. The general rule is that your notes should never cross the "major beats" of the bar. In 6/4, the "major beats" are two dotted half notes, and so the double-dotted half note that crosses this boundary is needlessly confusing.
Instead, use ties to "restart" the note at the beginning of the second beat while indicating that it is to be held:
X:1 M:6/4 K:C L:1/8 (2 FF z F2- F4- F z | F6 (2 F2 F2
The initial duplet in this version also has the advantage that it crosses two "minor" beats (the quarter-note subdivisions of the dotted half-note "major" beats.) I would personally find the following easier to interpret:
X:1 M:6/4 K:C L:1/8 F>F- F z F2- F4- F z | F6 (2 F2 F2
This is equivalent to the first version but also more clearly shows the subdivision of the first dotted half-note. (The quarter-note duplet also obscures the subdivisions in the same way, but it is easier to interpret since it takes up the entirety of a "major" beat, so I'd be inclined to leave it as it is.)
I'm just adding some detail re. @MichaelSeifert's answer.
The first measure is confusing, but the values all add up to a full measure. But because the major beats aren't notated in the OP's example it's hard to read. Below is how I got the final notation step by step from two major dotted half note beats, to quarter note subdivision, eighth subdivision, ties, then finally the duplet on beat one.
At first all the ties may seem busy on the page, but the point is to visually show the major beats. If you think about beating time with your hand, visually showing the major beats helps you keep track of the down beats you are keeping with your hand.
Given the compound time signature, I would expect a duplet to apply to the groupings of three, for example...
...I don't mean that is the only way to use a duplet, but it's the basic example to demonstrate it.
But the duplet is only on the first beat and one half. Wouldn't it be easier to read with a simple tie?