Hubert is Philip de Malvoisin's hunting master. It's his job to make sure the local peasants (and Saxons) don't poach the animals that Malvoisin has reserved for himself on his lands. This minor Norman character also appears at the Ashby-de-la-Zouche tournament in an archery contest against Robin Hood/Robert Locksley/whatever he's calling himself at that point. Hubert loses to Robin Hood (who's a legendary archer after all), but Robin Hood compliments him on his skills and courage. So that's an example in Ivanhoe of the English getting along with Norman commoners (like Hubert). It's the Norman lords that cause so many problems.
Hugh de Grantmesnil is one of the local Normans, host of the Ashby-de-la-Zouche tournament. Ivanhoe unhorses Grantmesnil on the first day of the tournament. Grantmesnil also comes back to fight alongside Bois-Guilbert and Front-de-Boeuf in the pitched battles of the second day of the tournament. But generally he doesn't really do much to distinguish himself from the other random Normans like Ralph de Vipont or Stephen de Martival. He's just a background player.
The word "squire" can mean different things depending on the historical period, but in medieval knight terms, a squire is a knight's assistant. He helps the knight into his armor and does errands for him. (He would also have some military training of his own, so he could assist his knight on the battlefield.)
After the first day of the tournament at Ashby-de-la-Zouche, where Ivanhoe has defeated five Norman knights in jousting, he gets a visit from each knight's squire. (One of them is named Jocelyn, but that was a guy's name back then.) The five squires offer Ivanhoe the armor and weaponry their knights were using when Ivanhoe defeated them. Ivanhoe allows four of them to just give him a bit of money instead of armor as a prize. This is a huge deal, since armor would have been much more expensive than a few coins for these guys. But from the first squire, Baldwin de Oyley, Ivanhoe refuses any kind of prize. The point of this prize thing is to show that honor has been satisfied on both sides. Baldwin represents Brian de Bois-Guilbert, and Ivanhoe refuses to consider their duel over and done with. He fully intends to fight a rematch with Bois-Guilbert at another time, so he can't accept Bois-Guilbert's possessions as a token of his triumph.
Baldwin responds that Bois-Guilbert will be too proud to use that armor again, so Ivanhoe should just take it. Ivanhoe suggests that Baldwin keep the armor for himself, or sell it – whatever he wants – but he won't accept anything from Bois-Guilbert. Ivanhoe does compliment Baldwin for being a thoughtful and honorable squire, though. Does that mean he is doing a good job by failing to deliver the prize he is supposed to give to Ivanhoe and then making a profit off Ivanhoe's refusal? The laws of chivalry confuse us sometimes...
Ralph de Vipont is a member of the Order of the Knights of Saint John, which makes him a Hospitaller – a rival group of knights to the Knights Templar during the Crusades. He's a minor character whom we only see because Ivanhoe kicks his butt in jousting during the tournament at Ashby-de-la-Zouche. Like Hugh de Grantmesnil, he doesn't play much of a role in the novel.
These two knights are the marshals for the tournament at Ashby-de-la-Zouche, which means they basically act as referees for all of the fights and contests at the event. Their job is to keep an eye on the contestants and order among the audience. When Ivanhoe wins the second day of the tournament, they present him to Prince John and insist that he take his helmet off and reveal his identity. That's how "the Disinherited Knight" becomes Wilfred of Ivanhoe. Besides this intervention, these two don't play much of a role in the novel.