For passive skills, while there are a few really high checks, the vast majority of checks are 10 or below. Between your 4 companions, you can give the Watcher +5 to all skills by having 11 skill points divided between the 4 other members of your team for each skill. In order to provide the most maximums, you want to distribute them in a 7/4 pattern, where one person has 7 points and the remaining 3 members have 4 points total (7/2/1/1 gives you the highest minimum, but I'm not sure that's ever relevant). Distributing skills in this way gives your Watcher +5 on all of their checks, and makes sure that at least one companion has a minimum of +11 for every skill for CYOA checks. You are then free to distribute points on your Watcher for even higher checks or to take advantage of gear that scales with skills. Personally, unless I'm aiming to use a particular piece of gear, I like to distribute the skills evenly, netting out at another +3 at the end. Adding in Skill training, I have 9 baseline in all skills with Party Assist, and can use Inns, gear, pets or consumables to boost it higher in the rare occasion that that is insufficient to make a check.
Active skills are a different beast altogether.