Thank you to everyone for your thoughts/input. If you're interested then below are my thoughts.
After spending quite a bit of time on this, I have come to the following conclusions:
John born 1805 (1st son) in Northumberland. He seems to appear in all the census with that birth date and place of birth and also his age on death matches.
Jno born 1808 (2nd son) in Durham. I can't find him anywhere so can only conclude that either he went by another name or wasn't the son of William Tulip and Margaret Bones (Barnes in his case). As they had two later sons christened the same name and one was later known by another name, together with the fact that the child born after Jno was the 3rd son and there seem to be no infancy deaths for the one born in 1805, I think possibly that is the more likely scenario.
Again thanks for taking the time to read my initial post and for your comments.
Joanna
