Welcome to the forums and the ever exciting world of budgie ownership!
I'm glad you have decided to welcome these budgies into your home.
We can help you out in determining your budgies genders if you post photos of them showing the whole beak/cere area.
Generally speaking an adult male budgie will have a royal blue cere (cere is the upper part of the beak where the nostrils are located).
A mature female will have a dark brown cere when in breeding condition and a creamy white cere when out of breeding condition.
Even if you have mixed genders in your flock, as long as you do not give them anything that they could use as a nest, then all should be fine and the chances of matings and eggs are substantially reduced.
You can also house 2 budgies per cage if you are too overwhelmed by the 4 being housed together. This could also avoid potential fights in the future.
For now, just take your time in getting to know each of your budgie's personalities and as far as training goes, go very slow at first, just by sitting close to their cage and gently talking to them. As you get to know them, you can pick the budgie who appears to be more brave and curious towards you and begin to tame him/her.
I have successfully tamed many scaredy birds with the help of a pet bird who is super tame and bonded to me.
For all the info and tips on how to tame your budgies, check the stickies at the Training and Bonding section.
When clipping a bird's wings, it's best to do so on both sides because they could have problems when it comes to balance when trying to fly or jump between perches. Hopefully soon they will grow back those flight feathers.
Good luck with your budgies!