The first bike looks like an early 500 Pantah, from '79 - '81. It has the smaller front calipers compared to a 600. It has been heavily modified, so could have parts from other models.
The older bike looks like a 250 from the early - mid '60s. (I don't have much expertise on this era of Ducati). Ian Falloon has documented the history of Ducati's models, and would be a good resource to pinpoint the exact model.