See this (and maybe sign in) for further details:
Split-screen has always been an integral part of Halo and I personally believe it was a huge mistake to cut it out of Halo 5. It needs to be added ASAP to recover the lost fans due to the lack of local multiplayer (in both the form of Co op campaign and split-screen multiplayer).
I would like to play 2 player with my son.
There is an existing topic on splitscreen; please go there for discussing the feature: https://www.halowaypoint.com/en-us/forums/6e35355aecdf4fd0acdaee3cc4156fd4/topics/official-split-screen-thread-v4-0/27262665-037d-4b00-b3a8-5c4c4b07e168/posts?page=1
The support forum should be reserved for troubleshooting and bug reporting. Also, petitioning isn’t allowed on Waypoint.