Unpaid rent

Rent Arrears

My tenant has not paid their rent for January and is saying that they cannot pay this month due to financial difficulties. Their guarantor is the ladies Father and I have said I will have to contact him for payment. However, he is now retired and they have said he cannot pay.
Should I still contact him and is he still liable for payment as the guarantor? Also, I have found out that they have contacted a local housing association and are looking to get out if they are offered a place. Should I write to them and start legal proceedings?
Thanks
Nick