Yes, show support for your sister when you visit them. Make sure they understand that you are doing everything to support your sister. This helps make your sister more effective.
Unity between you is everything now.
I try to do everything and as much as I can to support my sister. There are 5 surviving sibling, 4 of whom are in agreement 100%. The 5th is only interested in what he can get from them. They supported him COMPLETELY financially for the last 4ish years. When they moved into the retirement center, they gave him Dad's truck, whereas, I bought their sedan. Point being, if they ever have to presence of mind to call him because they want to move home or get their car or another car, he will be an ally in any plan that gives him (more) money. He will lie to them about us & our motives. He's the sib that submarines anything good we are trying to do for and in behalf of them.