Retirement Question?

Dear All,

My father is nearing retirement and would love to come and retire here to be nearer me (his son) and grand children.

He is 60, with a 48 year old girlfriend who has a kid and they have been living together in the UK for 5 years.

He fulfills all the financial requirements. However, if he applies to come here to live with his girlfriend and her son in tow (he will probably attend international school somewhere here), will they be able to make a single application as a couple or will he and she have to make a seperate application therefore their applications be treated as two seperate issues? Also what type of visa should the son apply for; educational?

I have scoured the forum and have not found the answer.

Thanks in advance,

sgy