That'll be Fremontodendron californicum
are you sure that's cherry, looks more plum to me. Not that it makes any difference
Probably one of the yellow cultivars of a Philadelphus
I've see them listed as Scilla campanulata (Hyacinthoides hispanica) so assume a synonym. I didn't know they weren't for sale anymore.
good plan Janabelle
Not sure that there's a weedkiller that would kill sedge without killing grass
one of the sedges I think. Usually damp ground plants so improving drainage might help