Manipulative siblings are after one thing, they seek to control everything around them. If you have a manipulative sibling, you need to learn how to deal with them right away because any relationship that involves manipulation is headed for trouble. Your mental and emotional health depends on you recognizing and dealing with a manipulative sibling.
Next, you are going to need to look into how you have been playing into your manipulative sibling's hands. You want to sit down and create a list of things that you have done or not done that were designed to please your manipulative sibling. You also want to note how you felt at the time, stressed, happy, sad, resentful, etc. After creating the list, you will need to look at the actions that were taken by the manipulative sibling to see what buttons of yours they were pushing. For example, if you are a giving and caring person, your sibling might say that you are selfish and cold just to get you to act the way they want you too.
Many times people make excuses for their manipulative sibling's behavior, which is something that needs to stop. You need to stop making excuses for their behavior because that only enables them to continue with the behavior. For example, if you are blaming their behavior on their unhappy childhood you are just giving them an excuse. The manipulator uses these excuses, as a part of their manipulative strategy, so be wary of anybody who plays the victim regularly. Something else to watch out for is generous offers of help, money, time, etc. To manipulators these gifts always have strings attached, they are going to expect something in return, no matter how much they say otherwise.
You are going to need to distance yourself from your manipulative sibling, which in some cases is not easy to do. You are also going to need to start asserting yourself and telling your sibling no to their manipulative demands, just make sure you are doing it calmly and rationally. One way to start asserting yourself is to establish and maintain boundaries with your manipulative sibling, distance yourself emotionally so that you can effectively deal with their manipulative comments and behaviors.
Manipulators often tell lies and half-truths to get the things that they want. What you can do to help deal with your manipulative sibling is to challenge those lies and half-truths. Make sure that when you are arguing back with your manipulative sibling that you use logic rather than emotion. In some cases, it will be easier to end the argument by agreeing to disagree, just never back down from your position. You might even have to repeat yourself numerous times until your manipulative sibling will back off.
You will need to be prepared for your manipulative sibling to escalate their behavior in response to what you are doing. The reason for this is that they simply can't give up control without a fight. Your manipulative sibling will probably say many mean and hurtful things to try and get your to change your mind, but you cannot back down. You need to stand firm, don't get defensive and don't take the bait. In some cases, your manipulative sibling will see the errors of their ways and will learn to appreciate the benefits of a more equitable relationship.