While I am no expert, I think that if you keep 2 in a 10 gallon tank you will be ok, you will just have to keep a good eye on your water quality. Being that you keep a marine tank you should be able to handle that. I would do a 25% water change every week with a tank that small.
You may want to fill a couple 12 or 16 oz soda bottles about 1/2 to 2/3 full and freeze them in the freezer use them to keep the water a little cooler. I've had my tank up to 78 a couple times, I think as long as it doesn't stay up there too long you should be ok.
Make sure to keep the tank out of direct sunlight.
Also, Avoid the temptation to handle them. The oils in your skin can be toxic to them. always rinse your hands off (no soap) before touch them and make sure your hands are wet and rinse them again when your done. Newts can release toxins that can make you sick if you have an open cut on your hand.
Goto the bait shop or pet store and get yourself some night crawlers and cut them into peices no bigger than the newts head. I use a long wooden skewer and put the worm piece on the end and try to entice the newt with it. if they see it moving, they will usually go after it. I suppose you could also use tweezers. Avoid leaving uneated food in the tank, it will wreak havok on your water quality.
If you don't like cutting up worms, try blackworms, they are smaller but a little harder to feed. They make a thing called a worm feeder, it looks like a plastic cone with perferations in it. you put a few worms in it and they slowly drop out the holes. The only problem is that newts aren't the best hunters and by the time they find the worms they may have fallen through the gravel. One last feeding option is ghost shrimp. Some people say they will eat them though I have quite a few in my tank and I've never seen them eat one.