There will be six of us traveling from Heathrow to Russell Square. One person will be a few months post total knee replacement. We cannot travel by tube as we will have too much luggage for the steps at Russell Square. Any advice on how to get there as a group?
Thanks.

Try http://hotelbybus.com/

Hotel by bus is no longer in operation. I think your best bet is a car service. They do provide vans for larger groups. I can personally recommend the following. www.exclusive airports.com and www.justairports.com

justairports or similar is your only real option. Very easy being door-to-door, and much cheaper than cabs (you'd need two at probably £75+ each) or the Heathrow Express + a cab from Paddington (outrageously expensive)

" the Heathrow Express + a cab from Paddington"

...really isn't suitable for people with serious mobility problems and luggage. There are escalators and lifts from the train platform level at Paddington to the mezzanine taxi rank - but they're poorly signed, fiddly and often congested with abandoned luggage trolleys.

The most cost-effective way of doing this journey is for a couple to get a car (at about £40) from just airports or whoever and the rest to get the tube.

The tube-users are almost certain to arrive first.