Your father sounds like my mother. She calls both my sister and I several times per day from her BT landline to our mobiles and tends even to wait for the calls to go to voicemail and will keep listening, but says nothing, which is highly irritating, to have 10 voicemails with no message, plus she will have to pay for connection.
Her phone bills are in excess of �400 every quarter, even though she has a mobile phone.
I did see an advert on the London Underground for a company called Lyca Mobile. Maybe you can buy these phones for your father, brother and yourself. Apparently to call Lyca phone to Lyca phone is free and 10p per minute to oher mobile numbers.
http://www.lycamobile.co.uk/
If you can convince him to use a mobile, then perhaps you could put a block on him calling mobile numbers from his BT landline. My mother is 82 and manages to use her mobile, which is the most basic model.