Hi J.,
It's been a long time since I've dealt with your situation. My son was about 4 during the first Gulf War when my ex was deployed so I know what you're going through.
My situation was a bit different though as my ex was regular Army when my oldest was born and so he was often "missing" from the picture throughout the first four years.
For the four year old you can try reminding him that he's the "man" of the house while daddy is gone. That sometimes helps older boys deal with the separation and try to be a little more stable. Even the 2 year old can understand that "daddy wouldn't like X behavior", sometimes that helps too - just reminding them that daddy will be coming back and that they should be helpful/behave while he's gone because that's what daddy expects.
Other than that you will find yourself being more lax, more permissive, and more frustrated. There's no real way around that. It just happens naturally, in my experience. The stress of suddenly being a "single" mom and worrying about your husband is going to be hard to deal with, I won't lie, and sometimes you're going to just not feel like doing anything.
Try to find some time for you. That's extremely important to "recharge" your energy while you're handling two boys alone. Small children feed off your emotions, so if you're on edge, they will be too. Give a little on the things that are small - pick your battles, stay consistent on the things that really matter.
Schedules really help in this situation because the children can expect X and Y and it gives them some stability in a situation where things have suddenly changed. Most important is to reassure them that Daddy is only supposed to be gone for X amount of time. You might try putting together a calendar with them that they can mark off some how to count the days. Help them write letters/draw pictures for him to keep them feeling connected.
They may also be acting out because they're afraid. They don't know what's going to happen but they may understand it's dangerous. You can try some role playing with toys, get them some plastic army men and have them pick one that's special, that represents "daddy". Let them show you through play what's bothering them so you can address it. You can also use those toys to try to show them what daddy is doing in a general sense. If he's a civil engineer he's probably working on infrastructure, maybe helping to fix things like bridges/buildings/etc...
Sometimes children knowing what daddy is doing and that's it's helping other children (fixing their school, their home, etc...) will help them feel good and proud about what daddy is doing.
Also see if you can find a support group and attend with them. NG and reservists often put together support groups to deal with deployments, and it can help to talk and be around other folks in the same situation. It will also help the children to be around other kids in the same situation - sometimes they help each other without direction from the adults.
Best of luck. I know it's hard, and frustrating, and frightening and exhausting. It doesn't help much, but thank you for suffering through such a time while your husband serves his country.
As we used to say, "They also serve who pack and move". Without strong families to support the men and women of the armed forces those deployed would be much less successful.
L.