Please follow the following procedure. Your Uncle is correct, follow his guidance. link is given.
FAMILY GNEALOGY FAMILY TREE IN KARNATAKA
Please go online and apply for this application.
The link is under "Nadakacheri" website.
1- It will only cost you 15 Rupee Per Application.
2 - Ex : Lets say "dad" has passed away, and mom is applying for family tree certificate, you need to include mom's name and sibling's name while applying .
3 - You need to get the estamp paper number before you apply.
You can contact the Notary or Some typing location near notary, they will help you with the contents.The affidavits need signature from Mom and siblings.
4 - On the portal , you will find the documents to submit .
Voter card , Aadhaar card, Death Certificate, Pan Card, Rationcard documents should be enough for you to get this . You need to upload your mom's documents.
5 - On nadakacheri website, you will get attestation for the family tree. The attestation is done by the revenue officer.
6 - As all government departments work, you might have to pay something extra.
7 - You might get the documents in a weeks time.
45, Dharmaraya Swamy Temple Rd, Halsurpete, Nagarathpete, Bengaluru, Karnataka 560002, India