OK, so that second part was kinda on purpose. (Bug #1) After completeing the Dawnguard and Hearthfire DLC's, I went back to do the Companions quest line...and no matter haw many times I reloaded, the 1st quest was always "Hired Muscle", and they ALWAYS sent me to deal Marcurio in Riften. Problem is, Marcurio is my husband, and he now lives/lived with our children at Lakeview Manor. Anyway, he wouldn't fight me (just kept saying "what are you doing") so I just took him to a giant camp and let him get killed...then (Bug #2) I never got the letter saying he was dead and now I can't remarry! I lost 1/2 my income from his shop...how am I gonna feed my lit'luns? (Bug #3) Also, after I came back from the "underworld" with Serena, Shadowmere was GONE! Can't find her anywhere, and I've had that horse for about 100+ hours! I MISS MY HORSE! I don't know if it will do any good to ask...but a "Summon Shadowmere" spell would be amazing. You could just buy it from the Dark Brotherhood once you received the horse. As for the spouse problem...the easiest way I can think to fix it is to just add divorce. Maybe you need permission from a Jarl or something. I didn't want to be a black widow, but the bugs backed me into a corner. :/

That sounds quite bad set of bugs there im guessing the hired muscle broke because he was your spouse and changed location & Shadowmere has had problems with some people for ages as far as i am aware.

They will have a hearthfire patch out soon i should think

You can't remarry in Skyrim. Letter or not.

There are numerous reports of Shadowmare missing. You could try to go to another cell and wait 30 days. Then return to the pond where she rises from. Then again, you have a better horse with Dawnguard, IMO.