For the first photo, you should be able to sharpen it with just about any photo editing software, usually comes free with your computer purchase, but there are other free ones you can download from the internet. Also, it's a bit over exposed, which is something else the program should be able to adjust.

Ideas for improvement in the future:
Iron the sheet before hanging it, I can see the wrinkles (coming out of his head) and they are distracting.

Use a fill-flash. Either bounce it off the ceiling (if you have a flash with this ability) or if you have a pop-up flash, use a diffuser over it. You can spend money buying one or just find a light-weight piece of white cloth (like satin), and secure it over the flash with a rubber-band (I've been known to use a kleenex when in a bind, it's helpful!).
This will do several things for you. It will make the boys stand out from the background more. It'll give you a little more light so you can increase your shutter speed which reduces blur. It'll help reduce shadowing on the backdrop, which is also distracting. It will also give a shine/sparkle to their eyes that is appealing in portraits.
...since you probably are not used to using a flash in this fashion, I'd strongly suggest taking practice shots before adding the dog into the mix, they are sensitive to flashes and it may become agitated.

Have them hold the dog a little lower so it does not cover up their faces. And if possible, remove the leash and collar from the dog because the spots of color through the fur is also distracting.

One more... choose colors that make their eyes stand out, the yellow does not work, it makes his skin tone off. I think I'd like to see the older one in a dark green. The blue shirt is good, but it drowns out his eyes instead of bringing them into the shot, maybe try a blue shirt that is not so vibrant.

...yeah I know, it's a lot to think about! but...
Once the setup is done, the rest is fun, so enjoy!

... and post your re-takes, I'd love to see them!

ok, one more thing, throw the same color sheet over the chair he is sitting on, so it blends into the background, or preferably use a stool that has no back. You can pick up a small folding stool from walmart for $10.