Bolt two 2x4s horizontally to the wall studs on top of the vinyl siding using lag bolts. You could put a few washers on the lag bolts underneath the 2x4 if you wanted spacers to keep from crushing the vinyl. Then bolt the tv mount to the 2x4s. not on Vinyl but on wood.
Decreasing the distance between your deck joists means that your deck boards are secured in more locations, span a shorter distance, and help prevent any unwanted cupping or warping. This helps solidify the deck overall and helps hold the structure together more firmly.