CGT on gifted shares upon company sale

Hi all. My wife was gifted 5% of a family business a number of years back (2008) These shares entitled her to an annual dividend which we always paid our tax through self-assessment. Her parents are now selling the business and for some reason they have asked for her shares back for free (!) so as they can proceed with the sale. Does that leave us exposed to Capital Gains Tax? We never paid anything for the shares and I am just concerned we may be liable to tax and we are asked to give something away for free. We don't have visibility of the sale figures and the exact deal so don't even know how to value the shares and considering this is a family business, we have very little knowledge of the ins and outs as we were always at arms length. Any advice? Thanks

Hi ,
 

Yes as this is seen as a disposal and would need to be based on market value at the time of transfer . Thank you .