I know of these albums:

Martyn Wyndham-Read, Geoff & Pennie Harris, Arky's Toast: Maypoles to Mistletoe
Trailer Records LER 2092 (LP, UK, 1975)
Trailer Records LERCD 2092 (CD-R, UK, 2002)
w/ Geoff Harris: vocals, guitar
w/ Pennie Harris: vocals

Alistair Anderson: Concertina Workshop
Topic Records / Free Reed 12TFRS501 (LP, UK, 1975)
Free Reed Records FRRR 15 (CD, UK, 2008)
w/ Geoff Harris: guitar

John Kirkpatrick & Sue Harris: Shreds and Patches
Topic Records 12TS355 (LP, UK, 1977)
w/ Geoff Harris: guitar
w/ Penny Harris: second hammered dulcimer

Royston Wood & Heather Wood: No Relation
Transatlantic TRA 342 (LP, UK, 1977)
w/ Pennie Harris: vocals, hammered dulcimer

Sara Grey & Ellie Ellis: A Breath of Fresh Air: Songs&Tunes from North America
Fellside Recordings FE031 (LP, UK, 1982)
w/ Geoff Harris: vocals

Suzie Adams and Helen Watson: Songbird
Dingle's Records DIN 327 (LP, UK, 1983)
w/ Geoff Harris: vocals, guitar

Sara Grey & Ellie Ellis: Making the Air Resound
Fellside Recordings FE039 (LP, UK, 1984)
w/ Geoff Harris: guitar, bass harmonies

The Kipper Family with the New Trunch Coronation Band: The Ever Decreasing Circle
Dambuster Records DAM 012 (LP, UK, 1985)
Dambuster Records DAMCD012 (CD, UK, 2005)
w/ Pennie Harris: hammered dulcimer