James might be a bit more strategic. He could start by trying to charm the Dursleys, but if that didn't work, he'd join Sirius in standing up to them. Remus would be more cautious, observing the situation first and then using his calm demeanor to deal with the Dursleys.
The Marauders would likely have a very negative reaction to the Dursleys. Sirius, having run away from his own awful family, would not tolerate the Dursleys' treatment of Harry. He'd probably confront them right away.
Sirius would be the most hot - headed in this encounter. He has a strong sense of justice and seeing Harry in such a bad situation with the Dursleys would make him lash out. James would be more about showing off the good side of the wizarding world to the Dursleys, hoping they'd change their ways. Remus would try to find common ground with the Dursleys, perhaps by talking about the normalcies in both the wizarding and Muggle worlds, all while making it clear that Harry should be treated better.
Well, Daphne in the 'Daphne meets the Dursleys fanfiction' would probably interact with the Dursleys in a very cautious way at the start. She would be observing their behavior towards Harry closely. Once she realizes the extent of their nastiness, she could try different approaches. She might try to reason with them, explaining how wrong it is to treat a child like that. When that doesn't work, she could use her magical abilities to disrupt their daily routine in a harmless but annoying way, like making the TV constantly change channels or the kettle never boil. This would be her way of getting back at them for their treatment of Harry and also a way to show them that there are forces they don't understand.
He might be very angry with them at first for how they've treated Harry.
Remus might interact with the Dursleys in a very calm and collected manner. He would probably be polite, despite their rudeness.
Ginny might be very curious about the Dursleys at first. But once she realizes how mean they are to Harry, she would likely be confrontational. She may not tolerate their rudeness and might even hex them a little if they push her too far.
Snape would likely be disdainful towards the Dursleys. He has little patience for Muggles in general, and the Dursleys' mean - spiritedness would not endear them to him. He might use his cold, sarcastic tone on them, leaving them confused and a bit frightened.
He might interact with suspicion at first. Given what he knows about how they treated his father, he'd be on guard. But then he could be polite just to see how they respond.
Harry's brave and sometimes impulsive nature might mesh well with James's boldness. They could be like two peas in a pod, getting into all sorts of adventures together. Hermione's intelligence and rule - following side might be a bit at odds with the Marauders' mischievous ways at first, but she could also learn to loosen up a bit from them. Ron, with his loyalty and sense of humor, would probably get along great with Sirius, who also has a strong sense of loyalty and a great sense of humor.
They might start off as enemies. Sirius doesn't get along with his family, so he may not want the Marauders to have anything to do with Regulus. But sometimes, they could end up working together for a common good.
In fanfiction, the Marauders interact with baby Harry in multiple ways. James, being Harry's father, is extremely affectionate. He showers Harry with hugs and kisses. Sirius, on the other hand, is the fun - loving uncle type. He might take Harry on little broom rides around the house (using magic to keep him safe of course). Remus is the gentle storyteller. He shares tales of magical creatures and ancient spells with Harry. And Peter, well, he tries to be helpful in his own way, like getting Harry his favorite toys. Their interactions are full of warmth and a sense of family.
Well, it could be chaotic. The Marauders are known for their mischief. Sirius might be really offended by the Dursleys' treatment of Harry. James would probably be shocked at how mean they are. And Remus might try to keep the peace but also be appalled at the Dursleys' behavior towards a young wizard.