'Wifi-only' just means that you don't have your mobile data (if you have it) on the same contract.
It is unlikely that your neighbours will make a difference, so long as they just want to watch TV and make festive phone calls; but if you aren't sure, check your bill and see how much you have on your contract, and how much you usually use. If there is a lot of leeway between one and the other (which is definitely the case for us) I don't think you have anything to lose, and if ever you are in the same boat they are likely to return the favour. I wouldn't hesitate, personally - it's good to be on good terms with neighbours.