Claire, you need to be following some basic guidelines for bringing a new dog into the house as basically you have two dogs who don't know each other and they are BOTH needy at the moment as both are relatively new. Do NOT reward unwanted behaviour by fussing over them if they do things that are not acceptable. But they will need managing so as not to get into situations where they will try and fight. This means avoiding sharing toys, eating treats close together, even eating close together -- feed them in crates or at opposite sides of a room. They simply need time to gain confidence and adjust to both their new home and each other.
All this is normal behaviour but two dogs do need to be managed especially as both are unknown quantities and also need to establish where they fit in the hierarchy.
If they bicker then just take each gently, individually, and give each a time out in a separate room for five minutes or so. Don;t talk to them, scold, encourage, NOTHING, just quietly take them in for a time out and close the door and leave. Then after 5 or 10 minutes, release and do NOT look at them, greet them, fuss over them when you let them out. Just ignore for anpother five minutes or so then back to normal.
Also: it is perhaps better not to make too much of a fuss over either of them, generally. Too much attetnion can make them very dependent and expectant of your attention all the time. It is better to just ignore them and try not to make up for what you may feel has been their hard lot in life. If you respond to them all the time and give constant attention and sympathy, they will become very manipulative to have that level of attention all the time and it can even be quite overwhelming for rescues, though it is our natural instinct to want to do lots for them. But this is a mistake and will not pay any benefits as ime goes on. Better to have them be a natural part of the family with good behaviour expected, not demanding behaviour; ignore them totally when they are not doing what you expect.
I'd recommend having a read through some of the material here
http://rescue.cavaliertalk.com/rescue/your new rescue dog.html
And here:
http://www.cavaliertalk.com/phpBB2/viewtopic.php?t=2317
and also this info on fostering applies equally to adding a second dog to your home:
http://rescue.cavaliertalk.com/rescue/fostering.html