I've tried getting the younger ones to "read" or color or do some kind of quiet activity or have them feel like they're doing class work too, but I can't get that to last more than a couple minutes. Help before I loose my mind.
My kids have always worked with us. Include them in the learning. We do a circle time where we say the pledge, sing songs for the calendar and songs for weather. Your 2nd grader can enjoy it as well.
Then I have legos, blocks and some lacing cards along with worksheets (my 3 year old at 1 1/2 new the difference in worksheets and coloring pages) or workbooks that they can work in. If my little one wants to sit in on the older child's lesson I allow it unless they do not sit still and be quite.
They know if they disrupt they have to go to their room till the lesson is done. If you have a playpen you can use it the same way just put it in another room.
If you have a play room with a baby gate and baby proofing then you can also let them play there for a little bit at a time, only if you can see it though.
I think the thing that helped me most was analyzing exactly what we HAD to cover each day to ensure my kids were progressing. This ment throwing out my idea of school - lots of sit down, quiet time, and instead doing more practical schooling - and I signed my eldest up for time4learning as a fill-in, something he could do while I was pulling my hair out with little ones. He could work on his own, and we both felt like he was getting 'school' in where it wasn't some major hands on project the lil's could participate in. I, personally, have no idea how ginormous families do it. That's just what worked for us. With the fill-in we could work for just like 45 minutes one-on-one.
Also, by re analyzing exactly what you need to cover, chances are you have the same kind of time filler stuff public schools use. Stuff that doesn't really progress her learning in any way. Even with my 9 y/o and 12 y/o we don't do more than 2 hours a day.
Some days you get a whole lot done, other days you sit in the corner and babble incoherently. LOL
I keep the LOs busy, busy busy! I have little boxes of things for them to do. Books on CD, beads and strings, Big pipe cleaners to bend into shapes, duplos, things to stack, beans or rice and measuring cups and spoons. Just lots of really entertaining things that keep them occupied and their minds working while I work with the others.
Thankfully my littlest is finally 5 and he has schoolwork like his big brothers for some of that time too. I found that my little ones asked for big boy work much earlier than my first one did.
It probably depends on your schedule. When I taught 1st grade to DS, DD was 3. DS was able to read so I wrote basic assignments down on a marker board for him and would keep DD busy in the playroom or with a movie in the den so she wouldn't be distracting. We had a few breaks between subjects so DD wouldn't feel left out and so DS could refresh himself. It was a new experience for all of us.
I recommend those chunky wooden puzzles and coloring books or stickers to keep the little ones occupied so you can get the next subject started. If they take naps, maybe use that time to teach the more difficult lessons so it's quiet and she can concentrate.