Is it possible to merge a group of mirrors in google or move to a new domain without losing positions?

Question

Google

1) Mirrors from a group of sites in google
A question about an additional site mirror in google.
Example:
main-site.com - main mirror
zercalo-site.com - mirror (duplicate site main mirror)
zercalo-site.net - mirror (duplicate site main mirror)
zercalo-site.org - mirror (duplicate site main mirror)
Task add a site to google, indicate to the GoogleBot search robot that this site zercalo-site.com is a mirror of the main-site.com site. Same with other mirrors. At the same time, without resorting to 301 redirects.
The robots.txt option of the host descriptive: for google disappears - they write here searchengines.guru/showthread.php?t=97883
rel="canonical" - not relevant according to the Google documentationhttps://support.google.com/webmasters/answer/13906...
Who has this experience?
Naturally, you need a working solution, taking into account the preservation of positions in google
2) Is it possible to move to a new domain without losing positions in google?
I have such experience, when moving to a new domain, the position of the site in google sags.
They also write here . What are the consequences for the position of the site in the issuance of PS does 301 redirect? and in google help it says the following https://support.google.com/webmasters/answer/83106...
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The URL change tool tells Google the actual URLs of your pages, which allows us to add a new domain to the index. The index update takes 180 days. During this time, Googlebot crawls and indexes pages with new addresses.
Here they write https://inweb.ua/blog/change-domain-without-losing... not a word about the loss of positions in google.
About google and yandex filters spec-seo.com/seo-sovety-2015/filtry-google-i-yande...
As I understand it, the Sandbox filter is applied when moving to a new domain.
Any relevant information is appreciated, preferably in the form of a link.
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P/S - Today, 01/28/2017, I looked through the issuance of google and analyzed the site of competitors.
I came to the conclusion that they repasted the domain in 2-3 days in google.
Everything worked out HTTP/1.1 301 Moved Permanently, the adult-old.site/robots.txt file does not contain the Host directive: and this robots.txt file is excluded from 301 Redirect and is identical to adult-new.site/robots.txt
What a discovery!

Answer 1

I advise you to leave robots.txt open for moving (where the new host and the sitemap.xml file are indicated)

RewriteCond %{HTTP_HOST} ^old.com$ [NC] 
RewriteCond %{REQUEST_URI} !^/robots.txt$ [NC]
RewriteRule ^(.*)$ http://new.com/$1 [L,R=301]

and the positions will sag in any case
ps if the domain changes, then they will sag =)