I haven't been in your exact situation. I have reconnected with friends who stopped talking to me and my STBXAH 9 years ago because of his behaviour (I didn't know why at the time). It was a bit scary but I met with them anyway and I now count them as good friends.
Its such an emotional time for you and for your family and you seem to have so many self doubts. Who cares if you cry - I'd expect you and them to have tears because of high emotions!!
I too 'should' myself a lot - it is something I've been working on with my counsellor. You are who you are and you feel what you feel. Should doesn't come into it. I have to be aware when I'm 'should'ing myself into depression - I find it all too easy to do. Something Givelove said on the forum clicked with me - have a look at my sig line. It has kinda become my mantra. I have it on my screensaver etc. (Have I thanked you for this Givelove? If not then thank you. Your words have helped me more than I can ever tell you.) I am who I am, I feel what I feel and I've done what I've done and no amount of shoulding can (or should!

) change it.
Maybe its time to have a look at the first step again? Let go of the worry - what will happen will happen. It does sound as if your sister is looking out for you and cares! I hope that, once it is all over, you'll wonder what all the worry was about. Be kind to yourself.