Parvo Virus help noticing if dog is cure and when it's alright for new dog?

Okay, currently there are 10 dogs here(house sitting for parents) mine, my sister, and my parents(they are on vacation-long story short). Any ways, somehow the dogs got parvo and didn't find out until 2 of my personal dogs died. Tried to keep my third dog alive and died, yet 1 of my sister and 2 of my mom's dog including her 2 month old puppy survived. We also live in a 3 ache ranch, don't be fool we aren't rich parents send all coins in this dumb ranch and looks like **** but it's big!. Now my problem is my friend offered me his dog 1 year old cause he moved and can't have it. I'm due to pick it up in a couple days. The dog has all shots and all, but even with the shots it's not 100% protect virus parvo. Now the question i'm not 100% the current dogs are over parvo, but they seem fine, will they affect my new dog? and is there a easy way to clear parvo from the grass and if the dogs are still affect will clean it be useless? Please help me i don't want a new dog if it's highly risk of death!!!