OP, you are so embroiled in this obsessive blame and negativity towards your parents and sisters, particularly the one with SN, that you are either incapable to, or refusing to, see your part in this.
Here are a few things that are very obvious to me (and Ihave said some of them in your previous threads):
It's not your sister's fault she has SN. You say she is attention-seeking, but people with SN do require more attention. Some of their behaviours and needs, which they may have no control over, or poor control over, or little or no awareness of, may well be attention-seeking. My brother has Asperger's and ADHD, and outsiders would call his normal self and behaviour very attention-seeking. But he really doesn't know he is doing it, couldn't understand why it was attention-seeking and wouldn't be able to change it. He is a highly intelligent man with a good job and a family, btw.
You must surely be able to see how illogical it is to seethe that your parents don't notice that you are depressed, but then you list all the various ways in which you totally hide it from them. You talk about how they 'must' notice that you are depressed and yet don't show it. You cannot presume that they notice when you go to such great lengths to hide it. It is incredibly unfair to be angry with them for not noticing when you hide it. And you cannot be angry with your sister for taking all the attention, attention which you clearly want a share of, when you are taking extreme measures to ensure that no attention befalls you. You are testing your parents and setting them up for a fall.
You say they don't notice you are depressed but then you say their only reaction to it is to feel sorry for themselves. How can they react like that if they don't know?
If it's true they do feel sorry for themselves, then, although that must be upsetting and unhelpful, they are only human. You are from a culture where mothers especially obsess about their children, are trained to blame themselves and feel overly responsible for their children, and where marriage is the pinnacle of female achievement. They have three adult daughters still at home, unmarried, one they know has had depression in the past and might have it now and is a martyr who won't help herself (you), and another has SN, and will probably never marry and they'll have to look after her forever, and will be worrying more with each passing year about what will happen when they're gone. So it is understandable, even if it's crap, that they might feel sorry for themselves.
You say they should be able to tell you're depressed because you stay in your room a lot, don't go out and so on. But you say you are a loner, don't really have many friends, don't make friends easily, and you belong to a culture where females are more restricted than the norm in terms of freedom to socialise, and stuff like that. Thus, your habits and behaviour would just seem perfectly normal for you. Add to this your determination to hide your depression from them, and it'd be more surprising that they would guess you were depressed, not the other way round.
You sound like you are hoping and waiting for them to notice that you are selfless and thoughtful and a martyr, and they will fall at your feet crying and begging your forgiveness, and then they will give you the exact type and amount of love, attention and support that you need. This is never, ever going to happen. You can only change your own behaviour, no-one else's. If you want them to notice you are depressed, if you want more attention, if you want other stuff from them, you have to tell them, ask them, you have to behave in ways that make those things possible for others to see the need in you, or want to give them to you.
You say that they 'emotionally make' you feel certain pressures. I have had lifelong depression and know that this is one of the classic delusions of depression. Also, no-one can make you feel anything, you are responsible for your own reactions.
Your elder sister might be behaving like a second mother for several reasons: she might have spotted your depression and need for attention and be trying to help you in a cack-handed way. Or, she might be very frustrated at living at home at her age, and is trying to assert herself as an adult in one of the only ways that that can manifest itself. Or it could be a mixture. Or it could just be your perception.
You CAN move out. You could live on housing benefit, or a range of benefits (well, probably not under this bloody government, but that's another thread). You could do things very differently. You have a job, you love at home and rarely go out, you must have at least an adequate amount of money in your account. Yes, they might well guilt-trip you, and make your life miserable at first when you move out, or make changes, BUT... Whether you never try, or you give in if they act badly, or whether you make a success of it is 100% and forever YOUR responsibility. Yu can stay at home fuming about 'how' people should notice you, treat you, support you, and 'how' your sisters should and shouldn't behave, and listing all the reasons and excuses to put yourself off,but the long and short of it is, it's you who are choosing this life and staying in it. You who could choose it. Has staying at home fuming and coming up with excuses changed anyone? Changed the situation? Helped you in any way? No, and it won't do in the future.
I've had depression, and Mh issues, as I've said, so I recognise a lot of the thinking and patterns you describe, and believe me, most of the problems aredown to your thinking, the rest of it down to factors that you will never be able to control. So take control of your own life and mind instead.