Assuming they are on an F ticket, or BA Gold, they can use the FIRST Lounge in T1.

Don't bother with the T4 arrivals lounge as that would mean going landside. They can get some decent food in the T1 FIRST lounge.

To transfer from T4 to T1, just follow the Flight Connections signs - no need to go landside. The connections centre can get quite busy at times, but I belive there is now a Fastrack if they are travelling J or F.

Cheers,
Rick