I'm so sorry for your loss. I can't imagine the pain of losing a cat I had for 15 years. I have yet to lose one of mine, other than a few childhood cats that I had that ran away or I never knew what happened to them.
I bet you could find an older cat that is looking for someone just like you, that maybe lost their owner, and is used to being a quiet little lap cat. There are so many cats out there like that, just looking for a home, it make me so sad. Or if you are not able to do that, since you have two kittens, just give it time. The kittens have each other right now, and they will settle down one day, right now they are just little balls of crazy right now. And I would think it would take time to bond with them, especially after losing a cat that you had for so long. I have heard this so many times on this board, people adopt another kitty, and they still feel that pain of the loss of their former cat, and that it takes a while for that to ease up. I'm so sorry for your loss, I can't imagine how hard it must be.