Don't be so hard on yourself. People snap at each other all the time! There are some relaxation skills you can use when you are feeling tense, sometimes I have to close my mouth and bite my tongue(not hard) to avoid saying something I will regret, and put a smile on my face. Usually I can just breathe through it, and it passes.
Relationships with family can be hard.
Dealing with bp is a lifelong process, be kind to yourself.