Sub domains impact on SEO

Hi all,

I have two websites. Both are involved in healthcare, one is b2c the other is b2b I want to improve both DA's. One has a much higher DA than the other. Both are internally linked to each other.

I have been told the following by an SEO expert.

That if I put one into the subdomain of the other (both hosted of course in the same VPS host) that it will help both re SEO. That if I use canonical tags then I can post the same content in each of their blog pages, for these overcome SEO crawler issues, not least because they are tied together. That having a blog page in both is better than having a blog page in just one of them, as they each have different audiences ie b2c and b2b, and this does not affect SEO. That the same backlink going to each blog page is not a duplication that will cause SEO problems.

BUT other SEO experts say that the opposite of each of the above is true.

I am so, so confused, as to what to do next. Is there a definitive opinion to this conundrum? Thanks for your help