Short answer. Yes. Rule 9, Section 3(c) provides that when a claim states a common cause of action against several defendants and only some answer, the court tries the case against all of them based on the answers filed, and renders judgment against everyone based on the evidence presented — no separate default order needed.
What the law says
When a pleading asserting a claim states a common cause of action against several defending parties, some of whom answer and the others fail to do so, the court shall try the case against all upon the answers thus filed and render judgment upon the evidence presented.
Rule 9, Section 3 — Default; [d]eclaration of. Read the full provision →
The partial-default rule
Rule 9, Section 3(c), labeled 'effect of partial default,' addresses exactly your situation. It provides that when a pleading asserting a claim states a common cause of action against several defending parties, some of whom answer and the others fail to do so, the court shall try the case against all upon the answers thus filed and render judgment upon the evidence presented. So the court does not simply issue a default judgment against the non-answering defendants and proceed separately against the ones who answered — the case moves forward as one, against everyone.
Why the case proceeds against everyone together
The key requirement is that the claim states a common cause of action against the several defendants. Where that is the case, the answers actually filed by the responding defendants become the basis for trying the whole case, and the evidence presented at trial is what the judgment against all the defendants, including the ones who never answered, will rest on. This keeps the proceeding unified rather than splitting into separate tracks based on who bothered to respond.
How this differs from an ordinary default
This is different from the ordinary default rule elsewhere in the same section, under which a court may declare a single defending party in default and proceed to judgment based on the claimant's pleading, without necessarily requiring a trial on the merits. Under the partial-default rule, by contrast, the case is tried on the merits against all defendants together, using the evidence actually presented, rather than the non-answering defendants simply having judgment entered against them on the strength of the complaint's allegations alone.
What the non-answering defendants lose
What the non-answering defendants lose is the chance to have filed their own answer and actively contested the claim through their own pleadings. They remain bound by whatever the court decides based on the trial that proceeds against the defendants as a group, on the evidence presented, rather than getting a separate proceeding or a chance to file late once the trial the answering defendants triggered has moved forward.