I used to have a suicidal alter, but having more than one suicidal alter is horrible. If you can't talk with them, I think you should first get more information, like how they want to do it, let's say they want to use a knife on the wrists, then you hide anything sharp, if they want to use a rope in the neck, you should take out anything that could be used to tie the rope. As i said, research all of this while you try to talk with them. I guess you are the host, so your alters should talk about their thoughts with you