Marriage only helps lower your tax liability in certain circumstances, namely, if one spouse stops working his/her partner may claim the remaining tax credits but excluding his/her personal allowance, the second most common way is if one partner earns significantly more than the other, they can take the bulk of the credits to offset tax at the higher rate.
For a married taxi couple who earn similar amounts, it’s pointless.
But hearty congratulations on your forthcoming Union. I wish you both Heath and happiness.