ONLY "Default Aeroplanes" will show up correctly during on-line, Multiplayer flights........anything else will appear as a similar Default Aircraft
Unless a viewer has the exact same aircraft in his/her sim. In that case, it will show correctly.
One thing to keep in mind is that if everyone is flying really complex add-on aircraft with huge texture files and detailed panels, thjen the load on the user's machine can get heaqvy if thre are a lot of people flying that type of aircraft and YOUR sim has to display them all.
best,
...............john