introductions advice and tips?

So I have an old boy (2 years old, not neutered), his brother passed away a few weeks ago and we were devastated... I couldn't bear seeing him so lonely, so I brought two sweet 1 year olds last weekend. They are in a different cage right by his (close but not touching). It's been less than 48 hours. As of now, my old boy is very curious but also puffs up and hisses when allowed to come near the new boys' cage.

What should be my next step? I have a cat carrier, should I just pop all three of them in and go for a walk? Should I wait a few more days to have them get used to each other's smells? This is my first time doing intros and I want to do it right.... Any advice or tips will be very welcome

Thanks