The only two Christian Cemeteries in Bukit Timah that I know of are or were at St. Joseph's Church (Bukit Timah 9 1/2 miles) and Kampong Java respectively.
The Church in Bukit Timah is next to Boy's Town and it still stands with the cemetery at the back of the church. As for the Kampong Java cemetery, it is now Kendang Kerbau Women & Childrens Hospital and part of it is a park.
The only cemetery in Yio Chu Kang or off Yio Chu Kang is a Japanese Cemetery (Chuan Ho Ave), you could be looking for Chua Chu Kang Cemetery.
About two years ago the last of the colonial cemeteries was exhumed (Bidadari Christian Cemetery. All unclaimed graves or remains are still at the cemetery awaiting to be claimed. (hopefully they are still there). The contact person is Yeo Eng Chuan and his email is email@example.com (This cemetery is preatty close to Yio Chu Kang)