Cockatiels are great pets!

You asked about feeding... Birds need to have food always available to them. A pelleted diet is best (I prefer non-colored pellets). If your birds have been on a seed diet prior to your purchasing them, and you decide to switch them to pellets, you'll need to take some time to wean them. Some birds wean onto pellets faster than others. I've found cockatiels to wean pretty quickly (several days/couple weeks).

Fresh fruit and vegetables are also great. My birds love leafy greens hung from the side of the cage, apples, peas, corn, jalapenos, the list goes on and on. Birds definitely have their preferences. You may have to offer things to them time and time again to see what they like. None of my birds like bananas, however my friend's bird loves them more than anything else. Unlike Bonny's cockatiel, mine prefer vegetables over fruit. It really does vary from bird to bird. Mine also like pasta (I prefer multi-grain).

Birds can also be picky as to how they get their food. One of my birds will not eat fresh fruits and vegetables from a bowl. I have a couple hanging toys that I put her fresh food in and she eats beautifully from those.

You asked if males can be housed together... Yes, they can! A pair of males is what I usually suggest people get. Females are great, but their egg laying can be problematic. As for sexing, it depends on the color morph and the age of the bird. Some cockatiels can be visually sexed very easily, others cannot be sexed visually at all. Cockatiels can be kept alone, but generally keeping 2 together is better.

Toys are also important. Bells and mirrors are favorites! Bird toys can be expensive to buy, but you can make a lot yourself. Twine and rawhide string are great places to start, then just get creative. Old keys, large beads, and old dog tag, etc. can all become great toys. Birds can also get easily board with their toys so it's great to change them often. They can play with cardboard toilet paper tubes and things like that too.

They also love to be misted with water. (If you mist them in their cage, be sure to take their food out so it doesn't get wet.)