Their names are Earl Warwick and Earl Salisbury, but you can drop the "earl" if you want. These two pals only come around to Team York after a long discussion with him, during which he gives a little history lesson about who should be king. After he's heard York's claim to the crown, Warwick promises to "salute our rightful sovereign / with honor of his birthright to the crown" (2.2.65-66). Later, Salisbury boldly tells Henry that he "in my conscience do repute his Grace / the rightful heir to England's royal seat" (5.1.181-182).
These guys don't see themselves as traitors, and they go out of their way to make sure everyone knows it. They see themselves as loyal to the true king—York. We see that Warwick and Salisbury are upstanding guys. They want to do what's right—and what's good for the country. They help poke holes in Suffolk's story about Gloucester's death, for example, and they stand up to Henry when they believe York has the right to rule.