2 Internet Connections Under 1 Network?

i have 30 pcs hooked up under one network. all 30 sharing 1 internet connection. 10 of those are put in a separate room for certain reasons. but those 10 like to download and cause lag to the other 20 pcs. my plan is to keep the 30 pcs under 1 network but ill add another internet connection exclusively for the 10pcs. and the original internet connection exclusively for the 20 pcs. how can i do that? reason why i need all 30 in the same network is cause they all use softwares needed to be connected to each other locally.