Subdirectory vs. gTLD

[moon-boots]

So I am merging two ecommerce brands together and have decided to do so either under a Subdirectory or gTLD.

My aim here is to increase the quality of my SEO for the weaker site (this would be the second italic domain shown in A and B below), thus taking domain authority from the dominant site, while 301 redirecting all pages from the old domain which will hopefully boost the authority and rank for the merged site).

My options for the merged site are:

A. www.website.com & www.website.com/hreflang=en

B. www.website.com & www.website.com/us

Or a combination of A & B (below):

C. www.website.com & www.website.com/us/hreflang=en

Factors:

1. Option A and C results in a longer URL structure for the merged domain which has a negative impact on SEO, while Option B is much more succinct.
2. Both Option A and Option B are the same distance from the root directory, weakening the SEO credibility of the merged domain somewhat. While option C would be further still.

Here are my questions:

1. Option B consolidates Domain Authority, but do Option A and C do the same?
2. Will the first domain receive a boost in Domain Authority and Rank due to 301 redirects targeting the second italic domain?
3. Will any option cause duplicate content issues (some categories/products are identical on both sites)? And if so, how best to avoid them (having Google ignore the subdirectory/gTLD is not an option).
4. One website will target the UK/EU while the other will target the US, will the merged italic site be able to rank well in the US?
5. Are there any other ranking factors I have missed or should consider?

I know this is quite an advanced series of questions, so I would appreciate the opinions of others so I can make the most informed choice.

Thank you

[moon-boots]

A little bit too advanced I think... well, trial and error it is.