See Dissociative Identity Disorder, (formerly called Multiple Personality Disorder) in section 17, at http://www.ezy-build.net.nz/~shaneris Try "conferencing", a method by which all the "alters" can communicate, and hopefully, eventually agree on the goal of reintegration into a "monomind". In the short term, however, it would be highly beneficial to reach some form of accomodation, because insomnia and depression are linked, and these are detrimental to your health, which is no good for any one of them, so it is in their interest as well. Another technique is autosuggestion, (self hypnosis) using 2 cassette players, one for the induction, and deepening of the hypnotic state, together with the instructions, and questions for the alter responding, the other to record the proceedings, for later playback. This requires a fair level of expertise, so I suggest using the former, and finding a therapist with proven experience in the successful reintegration of alters. The links in section 17 should help with this. ~~~ INSOMNIA: Put your mind in a position where it wants to shut itself off, and sleep. See insomnia treatments, in much more detail than can be included here, in section 3, at ezy build, below. Use one of the relaxation methods, in bed, after lights out, on pages 2, 11, 2.c, or 2.i, but they can take some time to learn, (progressive muscular relaxation excepted) so learn and become proficient in their use during the day; an alternative is to use the EFT, in section 53, and pages 2.q, and 2.o, saying to yourself: "Even though I currently have a sleep disorder, I deeply and completely accept myself." (or choose your own wording) while you use the acupressure tapping.
Find out which works best for you, in the daylight hours, so you will be prepared, come bedtime. For many people, a good idea is to develop a set "wind down" routine for the last hour before bedtime, so your subconscious mind learns that it is time to put thinking aside, and prepare for mindfulness, (awareness, without cogitation/purposeful thought) or the EFT, in preparation for sleep, but the idea with mindfulness is to not even think about sleeping: just drift off, naturally, during exercising those techniques. I suggest that you try using the EMDR variant, below, prior to the mindfulness, or the progressive muscular relaxation, but after the EFT, if that method is chosen. Experiment, to find which combination works best.
(The following is a variant of EMDR therapy, which has been used successfully for those people suffering from Post Traumatic Stress Disorder, insomnia, and anxiety: it is easily learned, quick to use, yet can be very effective. It is easy to be dismissive of such a seemingly unusual technique, but give it a good tryout, for at least a few weeks, to see if it is effective in your case.). Prior to using either of the methods in the above paragraph, first sit comfortably, and take a deep breath. Then, without moving your head, move your eyes from the left, to the right, and back again, taking around a second to do so (say: "a thousand and one": this takes approximately a second). Repeat this procedure (without the words, although you can count, subvocally, if you like) 20 times. Then close your eyes and relax. Become aware of any tension or discomfort you feel.
Then open your eyes, and take another deep breath, and repeat step one, closing your eyes, and relaxing afterwards, in the same manner. Then, repeat the procedure one last time. Some people may find that this is all they need do. With experience, you may find that you can practise this with your eyes closed. I have found that the 2 - 3 minutes spent using the EMDR markedly reduces distractions to the relaxation process, and is repaid many times over. ~~~ See page Z.12, in section 2, and the rest of that section on depression. Locators are in section 1, and use your phone book, for the various associations of mental health professionals. Ultimately, though; your best bet is a good therapist.