It's not about the IP, it's about passcode. Most trackers are using passcode to identify Dl/Ul. And yeah, when you log in you using your home connection and home IP, not the seedbox one. So, unless you guys sharing the same home connection you should be fine with sharing seedbox with same IP.
"Won't work on some sites" may come from different reason, like client installed on seedbox not allowed on the site, or smth else. This all can be clearified by asking on IRC or reading the forums/FAQ