We have two sinks in our master bathroom that are tied into one cold line and one hot line with a splitter. Recently I replaced both faucets with new ones and know when I turn one side on the other side comes on as well. Even though it is turned off. What do I need to do?

when I turn one side on the other side comes on as well I think I know what you mean but I have to ask. Can you be more specific? Are you saying that when you run one side of the valve the other leaks water? Or are you saying that when you run one lavatory faucets the other turns itself on? Let's have more details. Back to you, Tom

Tom, if you think you know what's being said you are a better man than I. Just reread this for a 4th time and can't picture what's happening yet.