You can filter the pages by their FrontendRootNodeId. Every site has a different FrontendRootNodeId which you can get using "SiteInitializer.CurrentFrontendRootNodeId". You can see an example code below which gets the "Home" page from the current site only.
var pageManager = PageManager.GetManager();
var test = pageManager.GetPageNodes().Where(p => p.Title ==
&& p.RootNodeId == SiteInitializer.CurrentFrontendRootNodeId);
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