So wifi, must mean a wireless network - correct?
Yes, that is correct.
Question: Can my MacBook Pro be on 2 wireless networks at once?
one for the internet (shared with household)
one for video streaming to my iphone, using a video stored on my MacBookPro.
No. The MacBook Pro (or any computer) can only connect to one wireless network at a time. You can; however, access the Internet simultaneously while streaming connected to that single wireless network. You are just sharing the same overall bandwidth (think highway with lanes) when doing both.
currently if I use the video streaming, it means I have to SWITCH between "wireless network used for internet" to a wireless network/computer to iphone network I have setup.
Wi-Fi and cellular are two different types of wireless networks that use different technologies. Your iPhone is capable of connecting to both types of wireless networks. An iPod Touch, on the other hand, can only connect to Wi-Fi wireless networks. The data plan that comes with your iPhone is charged when you connect to the cellular wireless network, not the Wi-Fi network. Most Wi-Fi network are billed monthly and typically do not incur a data cap ... although some ISPs are now starting to do so.
If you are streaming from video source on your local network, your iPhone should not need to connect to the cellular network to access the source. Instead, it should be connecting to the Wi-Fi network to do so, which should not incur any useage penalties.