How about a little more on your setup. Are these 2 sites in the same Kentico instance? You mentioned using REST to get the content but then in the same sentence also mentioned using an XML Datasource webpart; which is it?
If they are in the same Kentico instance then you can query that site directly without the need for any XML datasource webpart, just use a repeater and specify the path and site name of the site the news/events are on.