The Heathrow Express runs between Heathrow Terminals 1, 2 & 3 to Paddington Station, which is about half an hour away from Euston Train station by tube (London underground) or by London bus number 205.
Check out this link - https://www.cheapflights.co.uk/search/flights-to-Manchester/from-Heathrow
Euston to Stamford Hill
From Euston -> Victoria line to Finsbury park (3 stops)
From Finsbury Park -> Bus #106 for 20 minutes, which stops outside Fountayne Road
He needs to buy a Day Travel Card as the buses don’t take money at all
Sandwiches: Tuv Taam - available in Kosher shops
See also: http://www.ddsandwiches.com