I am so excited for you! It's tough I know, but there is a way to make it work.
I am awful at schedules, but forget about keeping a perfect house. I would go through things oyu don't need (toys/clothes/dishes/knick knacks/clutter) and just get donate a few boxes full to goodwill... it will cut down on a messy house fast, it's amazing how well that works!
Then, just do a chore routine you and your husband can share together. My hubby and I take turns cooking every other night, whoever doesn't cook that night does the dishes. We do maybe 3 loads of laundry a week. I wash, sort... and we fold together when he gets home from work. I sweep, he vacuums and mops. We both do the bathrooms.
As for your 3 year old, he will get out of that stage by the time your baby is born and will be a little more helpful. The 5 month old will be less needy.
Your heart and ability to juggle time will grow for your 3rd child. It is simply getting to that point that is the struggle!
For now, go to the Dr, get some Zofran, it will really help your morning sickness. Put the kids in a stroller and go for a walk, start doing small maternity excersizes, not only is it good for baby and your body, but it will help you gain more energy as well.
If you can enroll your oldest in a mother's day out program 2 days a week, or have a friend watch him for a few hours a week so you can get things done and rest, it will help greatly as well as help him develop as well.
As for time for multiple children, we take turns giving them individual time during the day and night, then be sure to have lots of family time as well. I take one child grocery shopping with me, it's date time for that kid and errands for me, then we go for ice cream. We rotate which kids gets to go, and my husband runs errands with a kid too.
Also, it's important to have a weekly date night! We usually put the kids to bed and snuggle up, eat healthy snacks while watching a netflix tv series or a rented movie, or just reading the scriptures together and conversing on spiritual matters and things that are important to us and ways we can implement being a better family.
It's a balancing act, but it's worth it.