Regarding seniority.
We have just integtated former TWA pilots into our list. I personaly lost 600 numbers so it's very tough to do without making alot of people angry. Since we have 12000 pilots and they have 2400 we used a ratio of about 8to1 in integrating about half of them and the rest ended up on the bottom of the list as of date of acquisition. They aren't happy either.
We also instituted alot of fenceing regarding base and equipment. For example: We can't bid STL until Jan. 2006 and they can't bid out of STL unless they get displaced. They also won't have access to 777 or A300 for a number of years.
It all comes down to career expectation prior to merger. A similar solution might work between LX and SR. No matter what you do though, it's going to be a mess. It always is. Good luck.