Tennant Advice

[roseplace1968]

Hi, could any one give me some advice please. My son and his girlfriend rented a house in october 2008. The letting agent wasnt very good they kept givng them dates to move in and then telling them they couldnt because the gas safety check and repairs hadnt been completed, they were desperate and eventually moved in after they got the gas safety done but not the repairs. The kitchen draws were falling apart, there was no shower upstairs in the en-suite, some of the ceiling lights looked dodgy and the list goes on, however they said they would do the repairs when they moved in, but they didnt so after a couple of months they stopped paying the rent and told them they would continue when they has done the repairs which they didnt. It has now come to light that the tenancy agreement was not signed by my sons girlfriend. She gave them 4 weeks notice and they have now moved out, but the letting agent has made no attempt to come and take the keys. What will happen over the unpaid rent and the fact they have not stayed the full 12 months, any advice would be appreciated. I am worried they are going to write to the gaurentor which is my sister and ask for the rent arrears, she doesnt know they stopped paying rent she will go mad.