4" speakers may need trimming to fit into the holes in the sei, i also had to cut a way a bit of the dash to fit my speakers, the depth of the tweeter doesnt really matter as the speaker fits to the speaker grill and has maybe half inch clearance from grill and speaker cone
a sei stealth shelf is available i had one, but i then made my own for a couple of quid, draw round your exsisting parcel shelf and cut it out, mark out speakers posisitions and cut them out, then cover in acoustic cloth
like chaos says the seats dont need to come out
the only thin that needs taking off is the trim, is quite easy to do, this pic might give you a better idea
the blue dots are roughly where the screws will be, there is also another screw in the back, just before the start of the rear seats underneath the seat belt anchor, there are 3 screws in total that need to come out.
once the screws are out the trim just clips off, may need a flat screwdriver to help it along the way
*post has been edited