Unfortunately I do not know the meaning of the names Wangechi and Chege. You may need to do a research by asking for the names' meaning from the elderly guys.
I will try and guess.
Chege is from njege. A smal njege is called gachege. Chege may therefore be a variant of a name of one’s who hunted tu-chege, njege, porcupines, etc.
Wangechi is a common and an old name but unfortunately it will be very difficult to get the meaning of that name, Wangechi. What is ngechi, gachia? Does it have anything to do with preparing food and the food is below what is expected? ... I don't know.
I will research and let you know if I get the proper meaning of the names.