Qualification to the knockout round, in the event that Holland win and Denmark and Portugal both lose, will be decided first on head to head and then goal difference. Head to head in this case concerns all three teams. All three would have an equal amount of points in that scenario. Denmark beat Holland but lost to Portugal. Portugal beat Denmark but lost to Holland. Which means that it'll be decided on goal difference instead, and Holland will have the upper hand there if they win by at least two goals tonight. They'd have 0 or higher compared to Portugal and Denmark who'll end on -1 or worse.
Basically it's a shit group. No one except for Germany deserves to qualify from it.