bank guarantor

I have a guarantor on my mortgage in Spain,if I default I assume the guarantor will be liable,he has little liquid assets due to having one of his houses already granted dation but has one heavily mortgaged spainsh property remaing,Would my bank be able to enforce a repossion on this property in payment for the guarantor status even if this is mortgaged to another bank?

The simple answer is "yes".  If you have a guarantor, the bank will come after you first and, if that fails, they will come after the guarantor fairly quickly and will treat him as if the mortgage were in his name.  That will include getting a court order to transfer any liquid assets in Spain to the bank and can require repossession too. 

how is it possible to reposses a house which is already mortgaged  to another bank? he is not in default with them and there is NO  equity in that house as it is now valued well below what is outstanding on the mortgage.