How many computers and/or iPads could connect to a single Internet home service before it slows down to a crawl?

I have Internet service from Clear, unlimited and as far as I know it’s 4G. We have two laptops and one Sony PS3 which we use to stream movies and TV shows from Netflix and Hulu. We don’t really use them altogether at the same time to stream. I would be surfing and my SO would be streaming without experiencing a slow-down.

However, the landlord’s kid upstairs has a new iPad and my SO gave her parents our network PW. During times when she goes to the net, and we are streaming a movie and surfing at the same time, would our signal’s speed be affected-?

If that happens, how would I know if it’s her iPad causing it or my internet service’s speed fluctuations-?

I won’t mind sharing as long as our normal set-up does not get affected. Thanks.