Definitely mountain bike!
From Kalk Bay it’s a short ride to Clovelly which gets you to ou wa pad (next to ou kaapse weg) from there you have noordhoek peaks, Tokai (arguably some of the best trails in SA) the beautiful mast climb. Can connect to newlands/kirstenbosch via the greenbelt trails, Table Mountain loop from there, missing link, back around chappies or on the trail next to constantia nek road.
If you don’t want to take ou wa pad to Tokai, there are loads of riders on main road going towards Tokai.
Also you can ride your Mtb on the road when doing the peninsula loop, Cape Point etc.
Throw in a wine tasting/breakfast for the rest of the family in stellies take the bike with.
