Best way to absorb discontinued brand/domain?

[NichGunn]

Our parent company is looking to absorb the domain of a brand we are discontinuing. The domain we want to absorb has a thousands of blog posts from 2010 onward. Much of the content is old but still high-converting. We would like to keep as much of the potential traffic as possible, but we don't want the parent website to become too large or lose credibility with too many 301 redirects. Any advice on the best way to do this?