Foreclosure would be based on the legal description as set forth in the Deed of Trust, NOT based on the Assessor's Parcel Number(s). The APNs are used by the County Tax Assessor's office for property tax purposes, but it is the legal description that controls in terms of your loan. Therefore, you need to look at your loan documents, and in particular, the Deed of Trust.
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.
I'm concerned as to how you separated the lots. Did you process a parcel map with the city or county in which you are located? If you didn't properly subdivide the lots (and just having separate APNs doesn't cut it), then the bank would still have the right to foreclose on all of it. Whatever the bank lent against, it would have rights to.