There's no way to automate adding people to WikiTree in the sense of adding 100 or 1000 at a time. Any way you do it will be one at a time. This could be via the GEDCompare process, which I've never actually used - search G2G for people's experiences of the system or ask someone who's used it for advice.
I don't know if this will help, but for my extension, WikiTree BEE, I put data into a JavaScript object and send it to the Add Person page as a parameter in the URL. Then I have code that looks for this in the URL to parse the object and fill the data fields. The way I'm doing it is scraping record pages on other sites (like Ancestry), creating the object with the data and sending it in a form with other parameters that are accepted by the Add Person page (https://www.wikitree.com/index.php?title=Special:EditFamily ): who (father, mother, etc. of), u (WikiTree ID number of an existing profile person (note that the ID number is different from the WikiTree ID which is Surname-123)), and person (the object). I only do this from record pages, because there's always a source/citation with the data. With your database, you could probably (if you wanted to go this way) do the same thing - create an object, complete with your citations, and send it into the Add Person page. Your fields can be automatically filled this way, but you'll still have to check the suggested matches for duplicates as you do when you're creating any new profile, but it's faster than typing everything.
Thinking out loud... Another way could be to make an API for yourself on your server so that on any profile, you could search your database for relatives of that person along with their relationship to them. Then you could click a button to go to the Add Person page with the URL parameters I mentioned before, and then fill the fields by calling your data in via an API call to your server rather than putting it in the URL, which can limit the length and sometimes have encoding/decoding problems. This might be over-complicating things, though.
