What is the best way to redirect for best SEO benefits? Examples: glaspunt.nl -> glas.nl fietstassen.eu -> loodgieter.nl Any technical information how to (root) redirect for best SEO practices?

Hi, we have several blogs and comparison sites on specific topics. All the domains rank on top positions in very competitive niche markets. We think that we can get more profit out of the domains when we put them under an umbrella brand. Customers that visit domain A can then also find products easily on domain B.  We see this for example on health.com, with several brands in the top. To maintain or improve our rankings i'm looking for specific information for the link structure. For example, is it better to have the 'about us'/rel=author on each domain, with contributors on that specific domain or is it better to have them all in the (umbrella) brand domain. At the moment we have the structure like this: domainA.com, domainA.com/blog, domainA.com/about-us  and  domainB.com, domainB.com/blog, domainB.com/about-us. I think to maintain the rankings it is best to keep specific content (like blog/ about us) on the domain. So is it the best to just do side wide links with a logo (like health.com) and what about hosting? We work with wordpress, so all domains will be hosted on one ip? when we use the multiple site option of WP? All information on this topic is more than welcome 🙂