Different score models used for joint mortgage application?
I'm applying for a second mortgage with my wife as a primary residence with a direct lender. I remember on our first mortgage (using a broker), our credit score report was given back showing the same credit score models being used for each of us and reflected pretty accurately. However, I just received the reports back for this application with a direct lender and it seems that the models used are different for each of us, which mine displays slighter lower of all models that I was able to access (Credit Karma: Transunion, Experian and AMEX: FICO). My wife's score displays significantly lower than I could access on any of those sites which would definitely result in a higher interest rate. The model also states serious delinquency negatively affecting credit score and there are no delinquencies on her credit from any reports I'm able to access and I know there shouldn't be because I help manage her credit/finances.
The models used were Transunion/FICO Classic (04) for her, and for me Experian/FAIR, ISAAC (VER. 2)
Is this normal practice? I'm confused as to why a lender would pull different models for different individuals on the same application unless it were to find a reason to lower the median score to offer higher rates (which sounds strange, considering how rates are plenty high right now and could result in DTI denials). If a broker is a direct lender, should I be trying multiple direct lender brokers or is that unethical to make multiple people work for only one to get paid in the end? Or does this only applies to normal brokers and not direct lenders?
I'm trying to learn as much as I can through our second time around and definitely don't want to be stepping on any toes here.