Hi my brother has narcissistic traits but is not a full blown narcissist

Thank you for your question. It seems you are confronting what you believe is the correct or caring thing to do and what you know you may have to do. When family are involved, or are the cause of difficult decisions, it is easy to get overwhelmed with our emotions and feelings. Sometimes changing the narrative from, what is right or wrong, to what is healthy or unhealthy, can ease some of the guilt associated with the decision.

You asked if you should cut him out of your life entirely, or continue to put up with him. There may be a third option. Have you thought about having a conversation with him to discuss your observations of his behaviors, how they effect you, and the possibility of getting help?

When you have this assertive conversation, you are putting the onus on him to decide if he is willing to do what is necessary for this relationship to continue. If he decides not to receive help or treatment, then that is on him, not you. You made a decision to continue the relationship, on your terms, so if he declines, then it is he who would be ending the relationship.

The difficult part is following through with your decision. This is where the healthy vs. unhealthy argument begins. Are there benefits to you if you choose to continue with the relationship as it is? Would you have less stress and anxiety if you continue with the current relationship? Are you keeping the relationship so others will be happy, or is it for your happiness? Would your mental and emotional wellbeing improve if you keep the status quo?

The answers to those questions will give you a better sense of how toxic or healthy your relationship is. 

The answer becomes clear if he chooses not to receive help, and there is no more deniability of how toxic the relationship currently is. Let those guide you.

Now the hard part. How to start the conversation. If possible try to start by saying nice things about your relationship. Then you bring up how you feel. The  most important step is to accept your feelings. You must accept you are going to have feelings and nothing is wrong with this. Feelings are not wrong or right, they only exist. Try not to get upset with yourself, rather remind yourself "I am feeling this way and that is okay." Pre plan the conversation. Write all of your feelings and thoughts down. Especially, if you have been suppressing or holding in what you have wanted to say for some time. If you don't do this, you may run the risk of quickly becoming angry, forgetting what you want to say, and becoming tongue tied.

Writing provides clarity, reduces deniability, and helps to organize and discovery what emotions are attached to your thinking. Most of all, remember this is for you, no one else. If it helps the other person or the relationship, well great, but those are only side benefits. 

If you have someone to role play the conversation with, that is a great exercise to prepare you for the real thing. I hope this provides you with some help.