Retirement tax questions

I don't understand this. How could we possibly put them on the deed after our death and what does "a step up in market value" mean?  We have an extremely low mortgage rate. We have to have means to allow them to live in the house or sell it. I do have an attorney but it seems there are tax issues I need to resolve before he can complete the will/trust.  We just want them to be able to keep the home.