It seems like you have your HTTP and HTTPS sites redirect to the HTTPS version of your www.example.com. This is good. Just know there is a cost for this initially.
In your case, only one sitemap will ever be seen. It is the HTTPS version of your www.example.com site. Any sitemap should reflect both HTTPS and www in the URLs that are listed. Any other URL will result in a series of redirects to your HTTPS www.example.com site which would not benefit you.
Most of the time, a sitemap is not required. It would only be used to compare pages listed in the sitemap to links and pages the spider will discover on your site. If a search engine can effectively crawl your site okay, a sitemap does nothing for you. There is no SEO benefit at all. Where a sitemap has value are for extremely large sites and sites where pages exist behind a paywall or login that you want indexed. That is it.
Whenever any site begins to use HTTPS instead of HTTP, the search engine will have to in effect start over. While this is not completely true in that domain trust scores and similar metrics remain, the HTTPS site is seen as a different site and all pages will have to be fetched, indexed, and any ranking for pages recalculated and earned again. For a period, the HTTP site will lose any search value while the HTTPS site has to gain search value. This just plain takes time.
While it is worth seeking a certificate and using SSL, it only effects a small sub-set of the sites trust score. Nothing else. It is not uncommon that SEOs recommend going this route as well as adding a sitemap. Seldom is it discussed when and where the value is worth seeking and the costs of such a change which is a shame. It often comes as a surprise to those who expect upward trends in search. For a site that is performing well, this change can disrupt performance at least for a period and potentially cost the site valuable assets in the short-term. Links to the HTTP site will retain value as long as the 301 redirects remain. This has to be discovered and recalculated. Each and every page on the site will have to be fetched, indexed, and have it's value recalculated as well as all of the search metrics site-wide. All of this takes time and for any site that was marginal in performance in the first place will see serious down-turns in it's performance that will take a long time to recover. Any site that was performing well will see serious down-turns in it's performance that will take less time to recover but still a significant cost to performance for a period.
I have always advocated not moving to HTTPS for sites that perform well unless needed. The site trust score benefit of going SSL can easily be made up for in other ways. If a site should be using SSL, then just know there is a cost to the process and be ready to take that on the chin. Please do know that I believe that SSL is a worthwhile effort in some cases and that there must be a cost analysis of the trade-off in order to determine if any shift to HTTPS is worth the effort. It is not something that should be done willy-nilly without regard to the cost of making the change. In the end, if any site feels that the change is a good idea, just know that there is a cost for a period and that for some sites, any trust value gained may not translate into better search results if the sites trust scores were strong as compared to the competition in the first place. However, making the move to SSL will make any site stronger as competition increases. This is good.