Dear Julio,
I agree you should probably seek legal advice, and don't be too concerned about the 7 day time limit. From the information you have provided, this time limit only applies to the "offer" that your wife's solicitor has made. So in other words, it sounds to me like the offer of 70% - 30% split will no longer be available if you don't accept it within the 7 day time frame. Doesn't sound like any great loss. It is open to negotiation, and you can make a counter offer.
The most cost effective way of reaching a property settlement is by negotiating it yourselves, however if you cannot agree and apply to the court to divide your assets then the court will look at the contributions and ongoing financial needs of each party and split the assets as it deems fair and just. Has your wife provided reasons why she believes she should have 70% of the proceeds from the sale? Did she make significant contribution to the mortgage? Does she have primary care of your children? These are also matters that a court will take into account if it is going to divide your assets. So try to think objectively about this and try to reach a consensus before legal fees eat into your assets.