I find it so strange the attitudes people have towards Wills and end of life generally. Death is a part of life and will come for everyone eventually, ensuring those you love are aware of your wishes and where to find that information is really important. Setting up Power of attorney is also sensible but that’s a separate issue.
I haven’t seen my parents Will but I know where it is should I need to see it. I know they will have given equal amounts to me and my siblings, whether that is the full estate or none of it. My siblings and I have no expectations of inheritance but we know our parents well enough to know whatever they have decided will be equal and that is all OP wants, to be treated the same as her siblings.
From what you’ve said @chillyolives it sounds like you aren’t entirely sure your parents have written a Will. This is really the issue you have, establishing whether your parents have made Wills and that they are up to date to reflect their current situation. If your mother pre-deceased your father, upon his death (if there is no Will) everything would likely be split between your siblings and you would be excluded because he is not your legal parent.
Every person over the age of 18 who has an asset or dependents should have a Will. Tomorrow is promised to no one and making life easier for those you leave behind by having your wishes legally recorded is just the responsible thing to do. Presuming things will just work out is naive, especially if there are more complex family relationships (divorce/remarriage/step children/half siblings/estrangement etc).
Dying without a Will is known as dying intestate and there are laws around how inheritance works in that situation.
https://www.citizensadvice.org.uk/family/death-and-wills/who-can-inherit-if-there-is-no-will-the-rules-of-intestacy/#:~:text=A%20person%20who%20dies%20without,under%20the%20rules%20of%20intestacy.
A Will isn’t just about who gets what money but also can dictate guardianship of any minor children, which it sounds like your siblings currently are and your parents should be making provision for what should happen if they were to die before they reach adulthood.
Wills can also express wishes about what happens with the remains of the deceased. It can be helpful to know this in advance to help with funeral planning at a time when most people are very distressed and may not consider to check the Will for instructions in a timely manner.
A Will can also clearly outline if a person has been excluded from inheriting intentionally. If a spouse/child/sibling has been left out of a Will and the courts consider they had reasonable expectation to inherit, a Will can be overturned if it is contested and does not detail a person was left out intentionally.
Wills also dictate the executors, not everyone wants this responsibility so it’s sensible for those writing Wills to establish the person they nominate is happy to take this on. It can be complicated, there are tax issues to deal with as well as notification of all relevant parties and services, a straightforward probate can take about 6 months.
Having open conversations about these subjects is important, no one knows how long they have in this life and making things easier for everyone else by getting a Will written is the best way to avoid complications and upset after you are gone.
@chillyolives I would suggest approaching your Dad and just asking if he and your mum have Wills as it doesn’t sound like your mum knows. I would then ask if those Wills include provisions for guardianship of your minor siblings to ensure that is sorted. If he says they don’t have Will I’d outline the reasons I’ve listed above as to why you are concerned about what would happen in that situation. This isn’t about being money grabbing it’s about being seen as your fathers child, which he obviously views you as but the law doesn’t.