What a big change doubling your family size! I can't even begin to imagine how tired you must be.

Can you homeschool your two oldest children, but find activities for them in the afternoon—not every day but a couple times a week? This will give you more time alone with the youngers, and your two oldest children will have your attention during schooltime. In the afternoon, the olders get social time outside the house, and you'd have time to bond with the youngers. Another option, do you have family and friends who would be willing to babysit? It's got to be an amazing juggling act making sure everyone's needs are met.

My wife and I found that putting our kids into one dropoff activity on the weekend really helped us as well. It's not super long (just 1 to 1.5 hours), but it gives us a chance to reconnect as adults and a little quiet. If she is on a business trip, it gives me time off from parenting as well—which is so very important for my sanity. Whatever you do, definitely look for outside help so you and your spouse have time for all children and yourselves as well.