I went through the application process for family visa. I had lots of queries and do see the same in various post. I touch upon the key elements: (India Context)
1. Certificates required: Marriage and Birth Certificate.
2. Attestation: In India get it apostilled. Does not require any Embassy of Oman or MoFA etc. Since India and Oman are part of the Hague convention, apostille is done by the Ministry of External Affairs India. And it is accepted. I used the services of Al Hind Attestations. In 2 weeks it was completed. Bought the documents completed in India and then couriered to Oman. In fact Al Hind and other agents have offices in GCC. So dont break the head. Just mention- For Oman
3. Bank statements- NO
4. Medical- GAMCA approved. Since my family was here with me already on a visit visa (we are UAE residents) I took the medical from Badr Al Sama (a local polyclinic). Pay OMR 20 and ask for "Visa Medical" They need only the passport in original. It takes 24 hours to get the report. If done in Oman, no attestation required.
5. And thats it. The PRO will get the requisite forms done and with copies and originals of the above, will apply for the Visa. The relatives joining visa costs OMR 30.
Trust this post was informative. Thank you for passing by!