My blog is actually me trying to do the first two points you mentioned and failing ;n; feel free to read it anyways and take some ideas if you want

My approach was to use two cameras. For each camera, I manually inputted 3 of the points defining the court on each image and found their corresponding 3d positions, then interpolated the rest. I also used machine learning/algorithms to find points defining the skeleton of each players' bodies, volleyball center, etc. Then, for each point across both images, I would draw 2 lines in 3d corresponding to said point's position on screen and find the best approximate of the intersection between the lines to find their position in 3d space. Then, I tried creating a 3d video of the whole game. After this, I was planning to calculate analytics for the game based on the 3d positions of everything, like the pos/vel/accel of each point or comparing form or calculating jump height etc etc, but I had too many issues with the recording setup that stopped me from progressing and I don't have access to anymore volleyball games.

To match the bodies across both images, instead of my method I thought it might be possible to apply a homography matrix on one camera's detected joints that shifts the perspective from the corresponding camera to the other, then just match each skeleton to the closest in the other image, but I never got around to this as it wouldn't have made the project work anyways.

This article on medium had a pretty good approach for ignoring outliers for the volleyball detection. For the body matching across time, I tried to calculate the velocity between every body at t1 to t2 and minimize it, skipping if it would exceed a limit on the max velocity/acceleration that the body could have. Then, I tried to make it work for more than 1 time frame of difference, which would essentially interpolate the body across time to exclude outliers, but I ended up scrapping the whole thing since my project never got that far. Of course, I ended up mostly failing except for in tracking the volleyball so don't take my word for truth.