I'm a single parent, but only have one child to manage. We've been traveling on our own to DL and WDW since my DS was 21 months old. Even with only one child, it's been tricky at times, especially managing counter service or buffet meals. But CMs always seem to know when you need an extra hand; Pinocchio even watched my DS while I went through a buffet line one time. It seemed to be most difficult when my son was 3-4 yrs old. I think the ages of your children will help; the youngest will likely not fight staying in the stroller most of the time, and the oldest will hopefully know to stay closed and be able to help support you with the toddler.
To your question -- I think the CR tower is an excellent choice. The Monorail is so convenient and saving steps will probably be very important since you won't be able to carry a tired 5 year-old and push a stroller at the same time (perhaps you'll use a double stroller?). The kids will love the monorail running through the resort, and Chef Mickey's is a fun and convenient place to dine. You can watch the electric water parade from the room after the little ones have nodded off. While any of the MK resorts would be great, I think CR tower will offer you the greatest convenience. If you do decide on another, you might want request a room that's not too far from the transportation.
From a security standpoint, I don't think you need to be concerned about any of the WDW resorts. However, the delux resorts will likely offer you and your DH a little more peace of mind.
It will be great! You'll have a wonderful time!