of course, with a right software you can easy to put multiple movie clips/trailers on a single DVD-RW disc, and that you can play them well in DVD player.
For your question 1, you shuold note, avi is a media container format which can be encoded with many different codecs, such as divx, xvid, mjpeg, h263, etc, so no dvd player can play all avi format videos on dvd disc, most dvd players only recognize standard video DVD well, can't play avi format videos on dvd disc.
For your question2, so easy, you just need to create a dvd menu for videos or scenes selection on your standard video dvd, to do that well, you can follow me to use RZ DVD Creator, it provide many dvd creation options, it can customize "play all", "titles/videos selection", "chapters/scenes selection" screens and buttons on dvd menu, can customize dvd menu background video, picture, music, text, etc, so with it you can personalize a cool DVD menu, it can burn mutliple movie clips/trailers onto a single DVD disc, it can convert any videos/movies to standard video dvd with the customized dvd menu, and burn to any dvd disc(DVD+R, DVD-R, DVD-RW, DVD+RW, DVD-R DL, DVD+R DL, etc), such as convert and burn 20 movie clips/trailers to a standard video DVD with a movies/scenes selection menu and burn onto a single DVD-RW disc.
Easy to use, insert a DVD-RW disc into your computer dvd burner drive, run RZ DVD Creator, select the dvd burner drive as target folder, directly drag and drop all 20 movie clips into the software, then press MENU button to customize the dvd menu and enable the dvd menu, at last press START button, you will get a good video DVD with the customized dvd menu from all movie clips, and you can play the burned standard video DVD well on your DVD player, and can directly choose the different movie clips and movie scenes to play. You can yahoo or google search RZ DVD Creator and download it, hope it can help you.