If you want cowls for the motors, see if you can get silver spray can covers and you can slide them over the square mount if they are the right size. Will look real cool.
Are you going to launch the smaller 4 engine plane from the larger. Notice you reduced the tail quite a bit. I give that a 50/50 chance of clearing.
Suggest you launch by building a cradle at an angle of about 15-20 degrees and retain plane at 2 points to keep it from flopping around in the air. I used a metal arm servo slotted (gear switch) and a upright wire between elevons to keep it stable. In fact, if rig is fixed to bottom plane, you should be able to used some power from dropable if there is not enough power to get launch vehicle up in the air comfortable when loaded.
Also, it is a pain to use 2 pilots, so get a Guillow's space shuttle, weight the nose slightly with tape and one wing and watch it spiral down. No need for other person.
Search here for my thread for my 3fer1 setup on shuttle. Any questions, glad to answer.