You can file any motions you feel are appropriate, but it's unlikely to be granted.
As the other answer mentioned, it's very common for the same lawyer or law firm to represent multiple defendants, especially when the defendants are related either through their roles in a particular situation (like appraiser, lender, and servicer all involved in the same mortgage). It doesn't necessarily mean that there's a conflict that affects you and your ability to move forward with the case. They may have conflicts among themselves if the appraiser wants to blame the bank and claim the bank is ultimately responsible since that would require the attorney to sink one client for the benefit of the other. However, even assuming such a conflict existed, it's an issue for those parties to work out and not one that directly impacts your ability to pursue your claims.
No, you can only move to disqualify counsel for a conflict with YOU, such as if this counsel used to represent YOU in a related matter and in the course of that representation, learned confidential information which prejudices you by allowing them to now switch sides and oppose you in related litigation.
Here, the fact that opposing counsel has relationships with the dismissed other defendants isn't a conflict of interest for them or for you, and it's not uncommon and is very practical for a law firm to represent multiple defendants in the same case.
But what's strange here, and maybe you misunderstood counsel's appearance, is that a lawyer would appear at a deposition for a dismissed party. If this lawyer the current counsel for the appraiser, and also the former lawyer for the bank, then that's fine. You were the deponent, so the depo notice would state which party noticed your depo, and if it was the appraiser, then that's who the lawyer was there representing.
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I agree that this is not the best place to put your efforts in this case. Even if there is a technical conflict (which sounds unlikely), the chances are that you are not the right person to bring it.
This answer does not constitute legal advice. I am admitted in the State of Arizona only. This advice is based on general principles of law that may or may not relate to your specific situation. Facts and laws change and these possible changes will affect the advice provided here. You should not rely on this advice alone, and nothing in these communications creates an attorney-client relationship.