Nothing is guaranteed when you move domains. I see the following risks....
we are launching all the pages again with new content, redeisgn
Yikes! New content might not be received as enthusiastically by the search engines. It might not be received as enthusiastically by visitors and they will bounce - sending a bad signal to search engines. If this was my site I would keep the content and the internal linking among the pages the exact same as it is now. If the rewrite is not done in a way that preserves the visitor's pleasure your rankings might fall.
These original sites... if they are popular and have a lot of type in traffic, a lot of branded traffic, a lot of brand mentions, a lot of domain mentions, a lot of good will, a lot of navigational search, then you will be walking away from that. Rankings can be supported more by these signals than by links in many cases. No guarantees.
We are in the process of moving 2 sites with higher page authority to another site we own
I believe that (generally) best SEO practice is done when the strongest domain becomes the host of the content. It then has the ability to pass its authority and reputation into the content being moved there.
**What is the health of these other domains? **
If you can't say that these other sites have clean link profiles, healthy content profiles, etc. then merging them could have some risk. It might pay to check these things out before merging. You know the story about "one bad apple."