Double topic. Refer to http://forum.mikrotik.com/t/bandwidth-rx-tx-on-interface/72468/1
On the interface, you can only set a limit to TX: routerboard can only control the amount of data it sends from the interface.
It might be sufficient with your needs, as your TX is your tenants’ RX (download).
If you need to throttle also your tenant’ upload, you will have to use queues; check this
http://wiki.mikrotik.com/wiki/Manual:Queue