Type of mortgage for buyout of sibling on property

I own a one third interest in family property and would like to mortgage to buy out a sibling who also owns one third of the property (to become a 2/3 owner). What type of mortgage should this be? Loan specialist is calling it a cash out mortgage which is slightly more expensive. Why is this not a regular mortgage? It is a purchase outright . . . I'm not borrowing anymore than needed to buy his portion. I understand the other party in the property will need to sign to approve of my getting a mortgage, but I'm not sure why this should be considered a cash out. The selling partner will receive the mortgage amount and be removed from the deed just as in any other sale.