Re: Deck framing question
Is it a hollow steel lally column or structural steel (box or I)?
If it's structural steel, simply attach a 2x12 on either side of it by drilling 1/2" holes through the steel and through-bolting with nut/bolt/washers. The steel will be trapped between two halves of the beam. You can add ripped blocks of wood at regular intervals between the columns so that the 2x12's can be attached to each other with more bolts.
If you wanted to do a super job, have 4 pieces of 3x3x14 angle iron cut and bolt them beneath each 212 as solid bearing to the steel.
If you have hollow steel columns with thin walls, you can proceed the same way, but to guard against crushing the circular-section post, you will need to fill them with cement before giving the bolts the final tightening. You could also box the lallys in with 2x4 and 2x8 to give solid bearing to the 2x12's. But they would need to bear of the footer unless you through-bolt.
Remove not the ancient landmark, which your fathers have set.