You will need another tank to quarantine the new axolotl. But after that, if you just want to see them in the same tank, or if the 30Gal has superior filtration, then you can make a divider very cheaply.
Introducing Juviniles to Adults on a Student Budget:
First you need a tank to house the juveniles for quarantining. I got a 32L underbed storage box from wilko for £3. Despite being only 32L, the dimensions are 53x17x33cm (LxHxW) which gives a large floor space that rivals that of a 60L tank. Remember that our bottom-dwelling axolotls dont care how tall the tank is as long as they can turn round! It's perfectly transparent and the lid is hinged which makes water changes and feeding that much easier. A few air holes drilled in the lid and you are good to go! (Assuming you have a filter for it).
After the 1 month quarantine period, you're keen to let your adult meet the juveniles but are worried about them hurting one another. You can make a fantastic divider for another £3! Look for 7 count plastic canvas on ebay, its a clear plastic mesh and comes in a variety of sizes. You should be able to get an appropriate sheet for around £2. Next look for aquarium divider suction cups, again ebay is your friend! You can get a pack of 5 for around £1 from hong kong so if you order them when you get the juveniles, they should arrive before the quarantine period is finished.
There you have it, £6 for a spare tank and divider that will allow you to easily introduce new juveniles to your adult tank. Compare this to £10 for an official aquarium divider and at least £40 for a tank with the same floor space (might be able to snag a second hand one for £30).