I have had multiple Arduinos and now a Pi or two reporting sensor data over HTTP. I used GET requests and gave each Arduino an ID in the query string, similarly each sensor it has has an ID too.
If you can get the sensor data to the Pi by some means, it can run a broker and echo the data to your cloud website as previously discussed. It might well be a valuable learning experience, but you may have to add some extra chicanery to get everything talking 