I'd personally suggest scoring better on the IELTS...
Showing proof of relationship is sometimes a real pain, as it involves other people providing you with their documentation, and subject to review by visa officers. If they're not satisfied that you meet the conditions of points claims for relatives, your application will be rejected as you're right on the fence when it comes to eligibility points...
Based on your current scores, all you need is half a band more in 2 sections (either listening, writing or speaking), and you'll get 67 points.
I'd say give it another shot. Many applicants do the same, as it's one of the straightest ways of increasing one's points...
Another option is to wait until you complete 6 years of work experience so that you score 15 points instead of the current 13. Two more points here.
Just between IELTS and work experience, you're missing out on 4 attainable eligibility points. I really think it's better than adventuring with showing proof of relationship with someone else (unless they're clearly your relative, but here there is a doubt). Only do that as absolute last resort, but you're really not at that stage yet!
Don't rush your application, do it right.