My situation is exactly like yours: homeschooling, DH and I having to share the desktop, etc. I also have a laptop but it's slow compared to the desktop... and I have dual monitors on the desktop which has spoiled me! We both fight over the desktop because I scrap on it and he animates. So, we have set up an agreement for sharing it which works most of the time.
I occasionally find time to scrap during the kids nap time. Of course, this means I'm not folding the laundry or mopping, or other chores I usually reserve for nap time. My 3 year old sleeps for 1-2 hours and my 5 year old will rest on my bed with books to look at for 30 minutes-1 hour. So, I'll scrap maybe 30 minutes and then squeeze in responsibilities. Then, I'll sometimes find a little time to scrap after they go to bed and before DH gets home from work. He has a long commute and doesn't get home until 8:30 or later. Finally, if it's my turn on the desktop I can scrap until midnight.
I can usually eek an hour or two out of the day this way.
Some days, the kids are playing peacefully and get absorbed in crafts or toys during their play time and I can sit on the computer a little. Our computer is in the corner of our family room, so I can pop on and off of it whenever they are playing nicely and aren't needing me for something. I have had to adjust my hobby to NOT have big chunks of time. I hardly ever scrap uninterrupted.
It's usually 10 minutes here or there.