It's Sow-en, Sow-in or Sow-vin very soft almost none existed v in the last one. But never any of the above. Sahween, shavnah, Sahwen are all mispronunciations. There's more about it further into the discussion if you're interested.
Easiest and right :)
Curious as to how you celebrate it everyday? Do you mean you keep the spirit of the season with you all year or something else?
For me each season has it's place though I do have favourites that I look forward to more.
Gaeilge/Gaelic was my fathers 1st language and I always heard him pronounce it as SIN has it stated above as sow-wen, the H is a silent letter in most Gaelic languishes, are many other letters. It can be used in some words but not in this case.
In the American language it is like saying that at times a Y sounds like an I; Example: Lynn/Linn and the second N here is silent!
Hope this helps, Blessings,