chain splitter and spare links/ jointers etc along with multi tool with pliers etc zippies, etc, spare gear cable + brake cable ??
– preride brake block check – If they're thin and it's gritty they'll be metal (yes that is over the top, car dead, stuck at gfs, bored)
extra drinks bottles and barley sugar/mars bars type bits
suggest an oval/circular route with start point dead in middle as it makes baling out easy and shortening easy – (maybe take extra maps etc so allow bailouts – but with only 4 I'd suggest sticking as a group).
Suggest a spare T per person and make last bit down hill/flat if poss (so they can swap Ts) – cold and wet generally means not enjoying (A black bin liner can have arm and head holes put in it and be a surprisingly effecive windstopper)
Change of clothes/pub/flask etc at end point (towel, changing blanket etc or pub toilet)
patience and tolerance
have fun