I think, you were unused to having a good salary, and wanted to be generous to family, which was really nice of you.
They on the other hand simply took advantage. You are not wrong to set a boundary so that they don't do this again and don't see you as the family piggy bank.
If your sister can't be bothered to talk to you after you helped her out with £3k she will never repay. Let her. Let her be like that. She's the one that is missing out on a good relationship with a kind and considerate sister, it is entirely her loss, although I expect it won't be long before she comes tapping on the Bank of Sis for another handout.
If you want to ... do some token presents.. A nice box of chocolates or something. You REALLY need to discourage the attitude that you are there to step in with a new PS6, or a new iphone or whatever unattainable thing they are longing for. Set a strict budget of £20 a head and no more. But really if they are not going to pay you back then you don't need to buy them anything. And I'd be making a note of which of them actually returns your money or buys you a present. You should go through your accounts and keep a record of what you've lent to them.. and mention the lack of repayment if they keep asking. Have any of them been particularly kind to you? I think if you say no to the next installment of free cash you will be able to tell from their reactions what they really think.
For your own sanity go see a financial advisor. .You should be focusing on your savings and investments, saving for a home and MOST importantly PENSION so that this money is not just sitting there for hand outs to them.
- Who would bale you out if you became unemployed or needed expensive medical treatment.
- What would you survive on if you got made redundant or don't want to go back to work after maternity leave for eg...
- or if you have future children.. this is money for their future.
You will have to be self reliant and you can't do that if you are bearing the financial burdens of your own family.
Invent some excuses.. "Its in a long term saving plan that I can't access" is a good one. "It's all gone into a works pension and I can't take it out".... "The company are having cut backs, I don't know how long I will be there." Anything really if you don't want to say an outright no. Or take the bull by the horns and say an outright no. Remember you never have to agree to anything at the time.. Let me think about it.. followed by a text with your decision.
And yes. You should cut the apron strings..It doesn't mean NC, but put more focus on building your own new life, making new connections... do you want to buy your own place?
Go on holiday over Christmas somewhere lovely. It will be much better than home with everyone wanting things from you this year. Sorry you are going through this, but maybe its a push on the road to independance and thinking more about yourself and your own future security, which is not a bad thing at all.