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I have a few older websites that SERP well, and I am considering merging some or all of them into a new related website that I will be launching regardless. My old websites display real estate listings and not much else. Each website is devoted to showing homes for sale in a specific neighborhood. The domains are all in the form of Neighborhood1CityHomes.com, Neighborhood2CityHomes.com, etc. These sites SERP well for searches like "Neighborhood1 City homes for sale" and also "Neighborhood1 City real estate" where some or all of the query is in the domain name. Google simply points to the top of the domain although each site has a few interior pages that are rarely used. There is next to zero backlinking to the old domains, but each links to the other with anchor text like "Neighborhood1 Cityname real estate". That's pretty much the extent of the link profile. The new website will be a more comprehensive search portal where many neighborhoods and cities can be searched. The domain name is a nonsense word .com not related to actual key words. The structure will be like newdomain.com/cityname/neighborhood-name/ where the neighborhood real estate listings are that would replace the old websites, and I'd 301 the old sites to the appropriate internal directories of the new site. The content on the old websites is all on the home page of each, at least the content for searches that matter to me and rank well, and I read an article suggesting that Google assigns additional authority for top level pages (can I link to that here?). I'd be 301-ing each old domain from a top level to a 3rd level interior page like www. newdomain/cityname/neighborhood1/. The new site is better than the old sites by a wide margin, especially on mobile, but I don't want to lose all my top positions for some tough phrases. I'm not running analytics on the old sites in question, but each of the old sites has extensive past history with AdWords (which I don't run any more). So in theory Google knows these old sites are good quality.