speed and bandwidth are near enough the same thing, if you have a bandwidth allowance of 200mbps that is the speed your router will have been allocated by the ISP. if you have 2 devices then both using bandwidth they will NOT get 200mbps each from the internet, they can't as the router would max out at 200 total.
The speed/bandwidth each device gets depends on a few things including the max speed of the network adaptor on the device and the number of devices connected. if you have two devices with 100mbps network adaptors then they will never get more than 100mbps, and if just one or both are using the internet then they could get the max 100mbps each, however if there are 5 devices using data then they wont get 100mbps each.
If each device has 1gbit network adaptors then the max they will get is a total of 200mbps from the internet as thats the max going to the router, the max speed between the router and each device may indeed be higher than 200mbps, but it will be throttled by the max 200mbps available to the router from the ISP.
Another way to look at it, turn on the garden tap with a hose connected and you will get water coming out of the end of the hose at x litres per second, now connect a T piece to the tap and connect two hoses to it, you will get x/2 litres per second of water coming out of each hose, the speed the water comes out of each hose is slower than if there was just one hose connected.