Q.trees
We bought a dwarf lemon tree. It has branches at ground level. Should we prune those or will the tree grow so that those branches are at a normal height for a tree?

You will want to cut those. These are likely below the graft union and are not the same as your dwarf tree. This is likely a wild citrus root stock. They will outgrow and outcompete your dwarf. They will also likely never bear an edible fruit. So cutting them off will save you disappointment in the long run.