So you have 2 x OH on the LHS and 3 xOH on the RHS. You balance an equation with parentheses the same way as with other equations. Parentheses separate calculations to be performed independent of a larger equation.
Over here I have two irons.
Over here I have two irons. The 2 outside the parentheses is multiplied by the implied subscript of 1 on the nitrogen for a total of two nitrogens and by the subscript of 3 on the hydrogen for a total of six hydrogens. First balance all atoms other than O and H. And over here on the right-hand side I have two irons.