दीवार पर परिवार की तस्वीर... (Family picture on the wall...)

सबसे पहले, यह पहेली सिर्फ English में रखने के लिए माफी चाहता हूं...

Special Note: If you succeed in solving this one, well and good; but in case, you don't, just leave a comment, and I will mail the answer to you...

At a friend's place, I was looking at a framed & mounted family picture of his, on the wall...

The picture contained - one grandfather, one grandmother; two fathers, two mothers; six children, four grandchildren; two brothers, two sisters; three sons, three daughters; one father-in-law, one mother-in-law, one daughter-in-law, one son-in-law...

So, keep in mind, that though this question may sound familiar to you, but believe me, it is not... Tell me, what is the minimum number of people required to be there in that picture, to complete all the above relations...?