"Now I have some of those fish that keep the tank clean in the water area . Is that okay ?"
Which species? Turtles make a lot of waste. Even if the turtles don't try to eat or pester the fish, they may poop them to death. So, I don't really think it's a good idea to mix fish and turtles in an aquarium but okay in ponds.
"Also how do we feed the turtles when we go on vacation ? Right now I give them the little pellets , but I just sprikle them on the edge of the water , and I give them small bite size pieces of bologna ,they love the bologna , it is cute how they come to the glass wanting the bologna when they see me coming into the room , is that okay to feed them that ?"
My hatchling page at
http://www.fishpondinfo.com/hatchling.htm lists some foods to feed baby turtles. If they eat pellets, those are good because they contain added vitamins, etc. Live foods like blackworms are a good choice for babies Bologna is usually rendered meat products that really aren't good for us or the turtles to eat. Since the sliders are babies (how big?), it's best that they are fed while you're away. Can you get a friend or neighbor to check on them and tend to them? If not, turtles can go days or even weeks without eating although it's not all that healthy for them. If you add live foods like blackworms, small fish if the turtles are big enough, earthworms as well as some aquatic plants like anacharis, they may be able to nibble off of those over a few days.
They will do better while you're away in the larger, 30 gallon tank. Only fill it with a few inches of water. The added surface area and volume will keep the water fresher longer and allow for any live animals you add to hide longer from the turtles (and thus spread out the feedings over a longer time). I could imagine if you had say 2" baby turtles and some pebbles, clay pots, rocks, etc. in there and then added a tablespoon of live blackworms, the turtles would be able to hunt and feed somewhat naturally over a week or so.