Hi,
in Maroc there should be no problem anywhere at all,however, in the more interesting parts, there really are some tough roads with steep descents and tricky corners, but if the local overloaded/overaged lorrys can cope with, your decent vehicle will surely do it as well.
The price of the ferry seems prohibitive to me. Have you ever considered the ferries from Sete (France)? They are surely more expensive, but you save a lot on fuel, road tax, accomodation and food and fatigue first of all, compared to crossing Spain.
Don't worry about children, if they are used to travelling, they will support and even enjoy it, in my experience, they are much smarter than their parents

Year after year, we are doing Hungary->southern Senegal without any major issues, the first time my daughter was only 3 months young!
The border crossing from Maroc to Mori is easy even in a 2WD, but take it slowly and as already said thousands of times, never ever deviate from the track! If you are not sure, better pay the 10Eur for a local to show you the track.
Peter