@Patricia, here are some realtor photos from the rest of the house (previous owner's furniture, not mine) In this one, you can also see the stairway paint color (could I simply extend that one into the living room?)

I have a 1964 mid century modern house I want to put on the market soon. It needs new paint colors to liven it up. Can anyone give me suggestions? Or a link to an app I can use that will allow me to try different colors just by uploading a photo? (no I don't have photoshop) Thank you!

If you can remove the popcorn ceiling, it will make the ceilings look cleaner and newer. Since you have children, you need to be careful to not generate dust, to keep them from developing allergies or asthma. https://www.google.com/amp/s/pulse.seattlechildrens.org/the-dangers-of-home-renovation-keep-kids-safe-during-repairs/amp/ Caution: some popcorns ceilings contained asbestos. https://www.google.com/amp/s/www.asbestos.com/blog/2018/07/24/asbestos-popcorn-ceiling-safe/amp/ The walls will have a better finish if you remove the wallpaper, scrub the walls to remove the adhesive (a wet roller mop works wonders) and then spray new texture to cover over where the adhesive was removed. Prime the walls and paint them in white flat paint. Then, using the same shade of white in a semi-gloss finish, put an extra coat of white on the woodwork (baseboards and doors). The screen between the dining room and hallway is non-structural. You can remove it but would have to patch the floor, ceiling and connection at the sidewall. Do everything white. If you don’t like the hallway, you can always find a way to rework it later with doors or cabinets. Sherwin Williams has 50 shades of white. You should be able to find a shade of white that is perfect for your home. They have a lightbox in the store that enables you to see the paint colors under different lighting conditions. Right now, they are having a 30% off sale: https://www.sherwin-williams.com/homeowners/special-offers/digital-media

I have a house that's very MCM on the inside and rather ordinary looking outside. we updated our garage door and it made a huge difference. (it's like the one pictured below, but in white.) I really like the mockups celerygirl posted. I think her ideas are going to be your best bet. you're not going to really be able to make your home look like a true midcentury, but improvements such those will make it look up to date and MCM inspired. I think funky landscaping can really help, and don't forget little touches like lighting.