So you can't find your ancestors so far in any of the online digitalised newspapers
Try searching the British Library Integrated Catalogue (see url below)
If you know where your ancestors lived in Britain and Ireland the online Catalogue should enable you to see what titles you might want to consult. The British Newspaper Library has systematically collected newspapers since the 1820's.
The collection doesn't pretend to contain every British and Irish newspaper ever printed. As the collection only stated in the early 19th Century, despite subsequent purchases, the collection is light for 18th Century and earlier material (hence look at the Gibson Guide or particularly London titles a good start is the Burney Collection). Also an estimated 6000 volumes of newspapers were lost as a result of bombing during World War II. Nonetheless this is one of the start points for any researcher.
The Catalogue won't enable you to immediately find your ancestors - you can search (using the name of the nearest town / city / county to where your ancestors lived) to establish a list of potential titles to research.