should I cancel the broadband I ordered

hi I’m in the UK and I have a question about the broadband I just ordered the problem is I live with my dad and we share Our internet for gaming online on our own playstation’s the problem is he got a crappy deal from talk talk so we have a lot of problems trying to play online at the same time but it’s fine when one of us isn’t and watching Tele or out at work so I asked if I could get and pay for my own internet and separate phone line installed and he said yeah ok no problem the thing is I just orderd bt infinity and told them I didn’t have a phone line so they said they will install one and for some reason for free but what I’m worried about I’s when the technician comes to the house if I tell him that we want to keep the current phone line and get the New one too will he say yeah ok no problem and install mine with no problems to the one we have now so my dad can use it and so I can set all my router up and everything or should I cancel it so bt don’t take me for all my pennys