Hi Leonie welcome to Roots Web, that what we are here for to help
The following information may be of some use.
It would appear that they are buried in Pathhead Feuars Cemetery
There is no Headstone for Birrell left in the cemetery
Perhaps they may have been removed in 1862, when the burial ground 
was levelled and the headstones placed in an orderly manner
John Birrell & Jean Wylie married 17.10.1813 Dysart
IGI gives a Jean Birrell born 10.12.1788 Dysart to Jas. Wyllie & Helen Bridges
Nothing in IGI for a birth of John Birrell
From FFH soc. Pre 1855 deaths Cd
Jean Wylie ( Birrell )  date of burial 31.12.1846 Dysart Pathhead
Age 57 Relict of John Birrell Manfacturer 
John Birrell  Feuar Dysart Pathhead  Manfacturer
Died Oct. 1832 husband of Jean Wylie
Pathhead Feuars Burials 
WYLIE, JEAN: relict of late John Birrell, manufacturer in
Pathhead; Dec 31 1846 (57 yrs) (Ri[t]chie, Oct 4 1849;
David Ri[t]chie, Dec 12 1854)
( must be the children of Robert Ritchie & Helen Birrell )
Pathhead Feuars Burial records 
http://fifefhs.org/Records/pathheadfeuars.htmIGI gives 
Helen Birrell married Robert Ritchie 11.12.1841 Dysart
Father: Robert Ritchie, Mother: Helen Birrell
Children: 
Alexander b 13 Sep 1842 bp 29 Nov 1842 Dysart
Jane b 12 Nov 1845 Dysart
ROBERT  b 17 SEP 1849 Dysart,
John b 2 NOV 1851 Dysart
David b  18 OCT 1853 Dysart
Could not find Helen Birrell on 1841 Census 
1851 Census
Dysart Fife ED 7
Hellen RITCHIE   33   Shipmasters Wife    b Pathhead Fife 
Jean   Dau  5   Scholar   b Pathhead  Fife       
Alexander   Son  10   Scholar b Pathhead Fife
Robert   Son  2   Scholar b Pathhead   Fife   
Christian  HALLEY Servnt   13  b Pathhead Fife 
Could be Robert Ritchies father
1841/426 Dysart -Fife Pathhead
The Knowe
Robert Ritchie  50   Blacksmith    Fife        
Jean Ritchie   30   Linen Hand Loom Weaver    Fife        
Anne RITCHIE 29   Linen Hand Loom Weaver    Fife        
Colin BINNAY  15   Labourer    Fife        
Margaret RITCHIE   9    Fife        
Jean RITCHIE  6 Fife                           
1851/426 Place: Dysart -Fife 
Mid Street
Robert RITCHIE      Head   W   M   75   Pauper Was A Blacksmith  b Kirkcaldy  Fife          
Ann  RITCHIE Dau  41   Bobbin Winder  b Kirkcaldy  Fife        
Margaret  YULE Grndau  19   Handloom Weaver  b Pathhead  Fife
Jean DOUGLAS  Grndau  15   Handloom Weaver b Dundee Angus 
Fraces   ADDIE Grndau  7   Scholar  b Pathhead Fife
Margaret RITCHIE Grndau  3 b Pathhead  Fife
Collin BAINIE Lodger  26  Carter b Kirkcaldy   Fife           
 You thought Helen Birrell had died her death certificate states
 Helen Ritchie died 29.9.1858 wife of a master Mariner 
At 10h 15 am Ravenscraig Castle Rocks usual residence Mid St. Pathhead
Age 41 father John Birrell Deceased & Jean Wylie deceased
Found Drowned 
Pathhead Burial ground William Pringle Undertaker
Reported by Isobel Ritchie Mother in law
No Headstone for Helen Ritchie
Could Robert Ritchie have remarried                  
1881 Census    21 Hill St Kirkcaldy
Robert RITCHIE Head Marr 64    Shipmaster b Kirkcaldy, Fife
Catherine RITCHIE 63 Wife (Matthew) b Kirkcaldy, Fife
Margaret RITCHIE W  daughter 34    b Kirkcaldy, Fife
Robina Ritchie SHARP grd daughter 6 Scholar b Boness, Linlithgow
Father: Robert Ritchie, Mother: Catherine Matthew
ARCHIBALD RITCHIE b 13 DEC 1841 Kirkcaldy, Fife
MARGARET RITCHIE b 13 DEC 1846 Kirkcaldy, Fife
ROBINNIE RITCHIE b 24 OCT 1853 Kirkcaldy, Fife
Norrie