Most cost effective way to pass Spanish property to your Children

My 65 year old Mother is about to sell a property she jointly owner with my Father (now deceased). Being over 65, I understand she is no longer obliged to pay CGT but will need to pay IHT in the region of 10,000 Euro as well as Plus Valia for which we are waiting for a figure from her Solicitor (he informs us this will be 'a lot'). Is there a cap on Plus Valia, i.e a maximum value. We are nervous as to what 'a lot' means, is this likely to be in the hundreds or thousands of Euro's? The property was purchased in 1990 for 112,000 Euros and is now selling for 310,000 Euros. Also, as this is likely to be her final Property purchase in Spain (and her main residence), can you advise the most effective way to avoid any unneccessary IHT or CGT for her surviving children in the event of her death? Would it be more beneficial for the property to be in joint names, that is owned jointly between myself and my Mother? Or indeed, in my sole name? I have read articles about using a Corporate structure to purchase the property but this seems overly complicated. Naturally, we do not want to avoid Spanish taxes altogether, we are simply interested in the most cost effective way to purchase her new property (which would be re-sale and not new). Many Thanks for any advice you can provide.