I can not prove to you that RC Sproul or anyone (including you)is a Christian, let alone Martyn Lloyd-Jones is a Christian.
However, I have a good idea that they are Christians, because of what they have written or said.

The Highway has many articles written by Martyn Lloyd-Jones, perhaps you should read some of these.
I don't want to speak for Pilgrim, but unless I am mistaken he would afirm with me that he (Martyn Lloyd-Jones) is a fellow Christian.
He obviously doesn't agree with his Charismatic leanings, but he wouldn't question whether or not he is a true Christian.