So sorry you are going through this OP, and hope that your mum feels more comfortable now that she is at home.
We unfortunately have family experience of life with cancer. It is hugely stressful, especially if the prognosis is uncertain or going badly.
It honestly sounds like your DH was stressed himself, and trying to do the right thing, albeit potentially clumsily.
However hard everyone tries, it is probably always going to be quite a shit time. The trick is to steal a few good bits for all of you. For us, that was sharing a pizza with DSIL in her last days at home and some games of Rummikub at the hospice. Other bits, not so much.
Have you spoken to DD about your mum's illness? It helped us a lot to talk to DS about what was going on, so we knew he would understand what was happening if/when we got upset or angry. There are some good resources on the internet about talking to children about a cancer diagnosis.
As for DH, I personally would acknowledge things got out of hand, that you are finding this really difficult and talk about how you can agree the logistics of the next visit in advance, to avoid this particular issue being a source of tension again.
