Simple answer is yes, it will have negative impact on your SEO. Why?
World wide web is all about the content, by redirecting to other websites your own domain will not have good content which can be indexed by Google and bring you more traffic. The other thing is if you write an article about the manual (so create content Inder your own domain) and then put ...
If the brands are related to each other, like an Apparel company who own multiple brand names, and the audience segment is the same, then you can go with subdomains.
Pros of subdomains:
Branding and niche authority are maintained.
You can more easily link between your various subdomains.
It is cheaper and easier to manage a website with one main domain and ...