Morning falconbird, we are 22 months down the line since my dh died. I am so sorry things are proving difficult for you and your sons, like others I would think they are grieving and perhaps are worried that they may upset you if they are jolly etc.
ours was a second marriage my dh was the love of my life, a great joker, very humourous and a loving Dad to 3 children and 3 stepchildren as well as all of the grandchildren.
when he died, we all sat down and agreed the most important thing was that we kept his memory alive, we have tears, smiles, reminiscing about life with him, we watch dvd's of past family celebrations when the grandchildren ask to see them (12 of them ranging in ages from 1 to 21).
we all feel free to show our emotions, when one is down usually the others are ok, we just support each other. Perhaps have them all round together and chat to them about how you feel happy at ghem speaking of their dad etc. The worst thing is when the family pussyfoot round us in case of upsetting us.
I do hope things will get easier for you all, this new life we are thrust into takes a long while to get used to for all the family.