The meeting would probably take place in a month's time, IC. I reason that would be enough to bring in the rest of the clan, clear away rubble, and secure enough of Blackreach for them to come and go safely. At the same time, Meesei would have brought in any scholars on the Dwemer from clans across Tamriel to study the place.
For Ahnasha and Fendros, if I'm remembering correctly, Ahnasha has been encouraging him to go to Cheydinhal to see his family. She might suggest to him to go to Cheydinhal, ostensibly to see his sister and allow her to be a part of the wedding.
As for the trip to Black Marsh, I don't think Meesei would find it necessary to enlist the help of another pack, since they are not undertaking a dangerous mission. Just a visit to Thorn, mostly. That said, she would have no objections if Sabine requested that Pieter come along. Pieter himself would be improving in terms of his mental condition, especially once he focuses on training magic. However, I think that "new love" feeling would start to wear off between them. Even in good mental health, Pieter does have some flaws.