I think unless a person is committed to the plan I would say no way.
You are starting the program and if the other family member said Yuck I'm not doing this ...It could Undermine your Progress and you will be in a fragile state and may sway your resolve! So unless both are committed to the program I say No!
Let the family member seeing you being successful and then if they want to start then they can.
My concern is this is not a program you dabble in...It's Full Speed Ahead or don't bother ..if the head 's not in it ...the chances of you getting the Awesome results that are achievable will never be fully realized!
My Hubby started 1st cuz My head was not in yet ..and I started 2 weeks later and I have been able to sustain a positive driven attitude.
So either all in no dabbling is my opinion.
Oh and being on it your taste changes ...so If I Just Tried It ... I WOULD HAVE SAID YUCK ! And been let off the hook!!
Good Luck,Roo2