Oh Pete,
That was a very hard decision to make. But, from what you described there was not way for you to make it. I am so sorry for your sadness. I understand how you feel. I am sorry that your siblings do not understand what you are going through with your RSD and everything else that is going on. Don't feel guilty, your step mom knew that you loved her and maybe that was not the way that you wanted to say goodbye. Funerals are very sad, you have fond memories of your step mom and those are the good memories to keep.
I am sorry for your loss and I hope that you are feeling better soon.

Sandy