Hard truth: Your siblings are more vulnerable to abuse. But that doesn't mean that they will be abused, nor does it mean that they are safe simply because you're being roped into being their caretaker. Your mother is worried, she has already lost a child and fears for them. But she isn't seeing the bigger picture here including what it will cost you (and them) for you to be a caretaker when you don't want to and don't have the emotional capacity (seriously, google caregiver fatigue). Your siblings need to be connected to any and all relevant services now. Depending on where you live, the options may look different, but there are options. Not signing up to be their full time caregiver does not mean abandoning them. I used to work with adults with developmental or intellectual disabilities who had survived abuse. What I will say is that depending on your area and available resources it is possible for them to live in a adult family home with other adults with ID/DD, it is possible for them to have a caseworker who actually cares about them and will follow their case for years, it is possible for your mother to visit them now and see that they are taken care of and to get to know the people who are taking care of them, for you to continue to visit them even after she has passed, for you to work with a highly credible agency, see background checks, etc. It is possible for them to attend groups, to acclimate to a group home now (while they have the support of their family and can also have sleepovers and trips home), etc. Healthy, well educated, well paid, well trained, professional caregivers will likely do a better job taking care of them then they every will. I would strongly suggest that you all to shop around and pick the best situations for obtaining this now.

The worst cases I saw in that job were people whose families sheltered them so much so that they weren't able to cope when the families were gone or who assumed that one person could carry a huge burden alone. Even in situations where someone had stepped up to be a lifetime caregiver unplanned for things happened (example: the caregiving sibling in their twenties suddenly gets cancer and a group home has to be found at the last minute with less options available and much more sudden change). The best cases/ the ones with the least potential for abuse were actually the situations where the family didn't wait until a crisis or a death and actually started to set up options while everyone was alive and healthy (seriously I worked for one agency where the directors sibling was actually cared for by our agency). It really makes sense for you and your mother to talk to more experts now (including therapists familiar with these issues, case managers, social workers, etc.) and explore all the options. This gives your siblings time to slowly adjust to changes and for a group home to adjust to them. It also gives your mom time to manage her own fears. If they aren't doing well then you can pull them out and make a different plan if one is available.

Talk to your mom about exploring options, including options for them to get other care, for her to get support in caring for them now, for you to get support in caring for them in the future, etc. Then let her know, after you've seen the options that are and are not available in your area, what you do and do not have the capacity to help with. Let her make informed choices from the options that are actually feasible (hint: you caring for them as she is currently outlining is clearly not a feasible option). Do some research here, different areas have different services so if you are willing to relocate for college and bring them with you/ have them in a home near where you are going to school you may be able to find an area that will provide them with a better quality of life then where you are. Be willing to get creative to best use the services available for you and don't be afraid to reach out to experts and advocates. Get your mother some support now and an expert to talk this through with.

But still go to the school you want and live your life. Visit them when you can and want to. Don't feel like pursuing your dreams means abandoning them because it doesn't. You can still support them, with time, love, money, etc. without assuming total responsibility (if you chose to do so that is).