The rules for a surprise round, seem to be focused on the people being surprised. (They lose a turn) rather than being focused on the people doing the surprising (They get an extra turn)
The rules are clear, that each person in a group can be surprised, even if other people in the group are not surprised. So if a party is ambushed by a single stealthy carrion crawler, some members of the group will lose a turn (be surprised) and others will not (they get to act normally).
However, I'm not clear what happens if two groups approach each other, were some members are being stealthy and others are not.
For example, I have a Rogue who is being quiet and stealthy and rolls a 20 on their stealth check. The rest of the group however (Fighter and Wizard), is just marching along at a slow pace. They turn a corner, and see a group of 4 goblins, with a passive perception of 13. Do the 4 goblins lose their first turn because they are surprised by the rogue? Do the Fighter and Wizard get to act on that first turn?
Another example, Same two groups. Two of the goblins rolled a 20 on their stealth, and the other two rolled a 5. Are the Fighter and Wizard and Rogue surprised? (They lose their first turn) Or can they only attack the two goblins with a stealth of 5?