On the "Young Hearts" quest after meeting Janett back at Nelsion you have to -Return To Jack, my problem is Jack has disappeared, their is no world map marker and the local map marker dose not lead to Jack. I also can not find Loyal and seeing as he hangs around Jack makes me think the game has glitched up.

Also on the "ED-E My Love" quest the map marker leads me to the back door of Helious One where their is a head of invisible scrap and the Gibson dogs but no Old Lady Gibson and when I do travel to The Gibson Scrapyard the dogs are also their but no Old Lady. What's going on their?

Can anyone fill in the gaps with these two issues? Where can I find Jack and what is the connection between Ed-E and Old Lady Gibson?

Nellis, not Nelson.

As to Jack, once the quartermaster in Hoover Dam disappeared on me and when I used console commands to teleport to his exact location he was somehow in Zion.
So if he's gone, he might be completely gone.

But you could look through the bugs section of the quest on the wikia: http://fallout.wikia.com/wiki/Young_Hearts#Bugs