If I am reading this correctly it means Aus beat Peru 1 - 0 or better and France beat Denmark to 0 then we will go through.
For every goal Denmark score we need to beat Peru by 1 more .
Correct
As it stands, this is the table
France 6 points GD +2
Denmark 4 points GD +1
Australia 1 Point GD -1
Peru 0 points GD -2
In order for us to qualify;
France must beat Denmark. Margin is important, but not as important as the overall result. If France win, we have a chance, if France fail to win, we are fucked.
Subsequently the margin of victory then becomes critical in determining whether we qualify.
If France wins 1-0, Denmark have a GD of 0, assuming we also win 1-0 we also have a GD of 0. However, as we would have scored 3 goals to Denmarks 2 (Australia, Peru), we would go through.
If France wins 2-1, and Australia wins 1-0, Denmark goes through on GD of +1 to our 0
Insert other scenarios here.
You're correct in saying our margin of victory needs to be greater than France's margin of victory unless they are kept to zero, which I think is honestly quite plausible. France is a better team than Denmark and while they haven't been convincing, nor have Denmark. Except France has some quality options available whereas Denmark have very few.