I'm jealous of your 25 Mbps with ability to get 50 Mbps.
Figure 5-6 Mbps per HD stream. The streaming doohickeys will auto negotiate a slower connection, and if you're a real nerd you can throttle them yourself with quality-of-service settings in your router.
Sports packages like to negotiate exclusive deals, like NFL Sunday Ticket, so you can expect legal ways to stream to cost $$$.