there's no standard reason why alters wouldn't know about each other. DID varies greatly person to person but alters typically know of each other or know most of everyone in the system. alters know what not to expose the host to and what to erase because alters are formed with specific roles. if an alter is a gatekeeper, like Alex, they manage memories. it's their role in the system. everyone in the system has a different role which keeps the host functioning when they all work together. for lack of better phrase, these roles are essentially programed into the alter and they even affect personal traits. a physical protector alter might look built and tall and have an intimidating russian accent.
alters can often recall and discuss trauma out of ear shot from the host but keeping it secret makes it hard for that alter to talk about during therapy because while they are out in the body, the memories are blocked. they can at best talk about how they feel and how to manage those feelings. not every alter has to have therapy because not everyone is directly impacted by the trauma or even have anything to do with it. their role could be centered around something else like keeping up the body's health and hygiene if the host is neglecting it.
yes, in my experience, my therapists are not solely mine but also work through the individual problems of alters, whoever is out during therapy that day. often times session are shared. if an alter shows up, it's fair practice to give them the floor. while the alters assist with host's problems and keeps the host functioning, they also have their own lives and their own problems. alters can have anxiety, depression, dysphoria, trouble with sexuality, any problem under the sun because they are people with complex thoughts and emotions just like everyone else.
if an appointment or something important is missed, it's either because the alter didn't know, forgot, or didn't care. alters typically know enough about the host's life to know the importance of scheduling or can be co-con with the host in which they can have a conversation and the information can be shared. alters can pop up at work and if they're not a total dick, they'll see the work day through in a discreet and productive manner. in exchange that alter gets free time later. but of course this depends of your communication with the system and how willing they are to compromise and share. some are more willing than others. the better you understand each other, the better you work together. if you don't compromise, you will just end up fighting and then nobody gets what they want.
