I think you would have to run two queries, one TopicQuery getting the 5 last topics and one ReplyQuery getting the 5 last replies and merge the results, keeping the 5 last in total.
Another way of doing it is to set ChangeDate when you create a new Topic and then use that to sort your query. That way you will only need one query.
We want to list the latest posts in all rooms. The list should include both new topics and new replies then we filter out i.e the first 5 of that collection.
Can this be done using GetQueryResult? or do we have to first get all rooms and then loop through each topic?