I think some people have misunderstood the question. It sounds to me as though they have 2 nights in London, arriving late Thursday and not departing until Saturday. That suggests they are having dinner with their friend on Friday, in London.
And from what I have read it is indeed more convenient to get between Heathrow and London than to go from the Bath Road area or other so-called airport hotels into London, which they would do on Friday, both for sightseeing and to meet their friend.
So a London hotel with good access to Heathrow is called for. That suggests to me a hotel near Paddington and transport by the Heathrow Express, which is fast (15 minutes from LHR to Paddington) and not a problem either late Thursday; night (as long as it is not too late) or Saturday morning for the return to LHR. Note that the HEx trains run every 15 minutes, not quite as frequently as the tube, but I still think it is faster and more convenient in their situation.
https://www.heathrowexpress.com/timetable-schedule/heathrow-london
The Heathrow Express is avoided by many because of the expense. But there are ways to reduce that cost, namely by buying well in advance, or, for 2 traveling together, with a Duo Saver ticket which is a round trip ticket for two people.
https://www.heathrowexpress.com/tickets-deals/discounts-deals
As far as hotels near Paddington, we like the Indigo which is modern, close and reliable, and we can get a deal with our IHG points. But there are lots of hotels in the area, some better than others. Maybe someone can recommend others of those, which would be helpful to the OP.