I tried twice to post a pic as an example, but the website wouldn't accept it.. Just imagine one thick main branch and several short and skinny ones instead, please.

I prune/shorten the longest branches and it seems to help the smaller ones get more energy, I feel like. Are yours seed grown or grafted?

oops, you said seedlings :P

I would check the roots/caudex for rot. See if this web page helps: http://www.tropicanursery.com/adenium/problems.htm