Just to be clear, Seattle has a magic number of two (vs 49ners) to win the division [Cards and Rams are eliminated from the division race], and a magic number of two (vs NO/Carolina) for HFA.
Since Seattle plays the Niners this weekend, Seattle can win the division outright this weekend. Because that would make Seattle's record a minimum of 12-4, only the NFCS Champ could exceed it (either NO or Carolina) insuring the first round bye as well.
Seattle has the tie-break against both NO and Carolina, and if both teams could lose this weekend, Seattle could get HFA as well. Unfortunately NO and Carolina play each other this weekend which means one will almost certainly lose but one will almost certainly win (and both can't lose). That prevents HFA from being clinchable this weekend.
So.......
If Seattle wins (or ties) vs San Fran this weekend, Seattle clinches a first round bye and the NFCW Crown.
Assuming Seattle wins in Week 14 (which I think we will), Seattle clinches HFA in week 15 with either:
1. A Win or Tie
OR
2. A Loss by the winner of NO/Carolina from Week 14.