I am so happy for you!!!!
There is nothing more rewarding than a cat's acceptance! They can be so independent and aloof, you think they'll keep you at arms length forever. Then the armor begins to crack, and pretty soon you have a loving friend for life. Congratulations!
I'm looking at a line of wood cat trees that offer either sisal or manila rope scratching posts. Obviously they look different, with the sisal being a light tan and the manila being brown. But that's more a human option - I don't think the cat cares what color it is!
So I'm throwing it out to...
Some cats are just more aloof by nature, or he may have had some bad experiences. Or maybe he was taken from mom too soon. There are so many reasons why he might be hiding. Try to be patient and let him set the pace. If he needs you, he will come to you.
Patience is the key - and the colder weather makes most cats more affectionate. Let him come to you, let him sniff you - cats are very attuned to smell.
Bless your good heart!
You are an angel, and I think you are in for one of the most rewarding experiences of your life by adopting these two wonderful, beautiful boys! Their affection and companionship and entertainment value will come back to you one hundred fold!
I'm fully in the no bell camp. Watch a cat's ears - they use them constantly, dogs do too. They are essential basic communication and information. A bell may reassure a human, but a cat or dog - not so much.