Keep in mind, new counsel cannot swear to the allegations made in the old firm's pleadings, but the new firm still has a duty to report any suspicious or blatant fraud.
Bring it to the court's attention. Instead of saying: "Judge there is fraud everywhere - call the cops!", tell the judge: "I am questioning the validity of this document, and if opposing counsel has had time to review the file, I believe they will verify my suspicions.", and then explain why you believe the document is a forgery, etc. and can't possibly be valid or convey a right to foreclose or be granted any relief.
(This is not legal advice.)
Forgery is the process of making, adapting, or imitating objects, statistics, or documents with the intent to deceive. Fraud is the crime of deceiving another, through the use of objects obtained through forgery. However, copies, studio replicas, and reproductions are not considered forgeries. They may later become forgeries through knowing and willful misrepresentations. In the case of forging money or currency, it is often called counterfeiting. It is called a false document when the object forged is a record or document. Forgery is one of the techniques of fraud, including identity theft. A forgery is essentially concerned with a produced or altered object.
Generally, forgery is defined as the fraudulent making or alteration of a writing to the prejudice of another’s rights, or as the false making or material alteration, with an intent to defraud, of any genuine writing which might apparently be of legal efficacy, or the base of a legal liability. Forgery includes the alteration of, or addition to any instrument with an intent to defraud[i].
Uttering a forged instrument is a criminal offense. When a person knowingly publishes or puts into circulation any forged or altered financial document, legal document or other writing with the intent to misrepresent it as true and defraud others it amounts to uttering a forged instrument. To “utter” means to distribute or offer under the pretense that it is genuine. The uttering of a forged instrument is a separate and distinct offense from the making of it. The accused must not only know that the instrument was forged, but s/he must intend to defraud at the time of offering it.