Thank you for your question for Extension. It will be hard to diagnose the brown spots on your plants without pictures and knowing the name of your affected plants. Brown spots can be caused by watering, fertilizer, and light sources in your home. If you want to reply to this email and send pictures, I could help you further with some recommendations. 

To answer your questions, baking soda does not help houseplants, and aspirin probably won't hurt, but it won't be effective either. I would recommend neem oil only if you see pests, as that is only a pesticide. Here is a great article from Extension focusing on watering houseplant care:

Watering houseplants | UMN Extension

Thank you for the pictures. It helps me to pinpoint what the problem might be. Your plant is a dieffenbachia, which are known to be a challenge to care for. I had this plant a few years ago and it didn't make it. Here are a couple of ideas:

1. A common problem is watering and how it's done. They do not like tap water out of the tap, so I'd suggest filling a jug with water and letting it sit a few days before watering. I use a gallon jug and then add a dilution of fertilizer so it gets a little with each watering.

2. Be sure your plant doesn't sit in water and you have good drainage. 

3. Your plants roots may be water-logged if they've been overwatered. 

4. Have you lightly fertilized your plant? This is important to maintain nutrients in your soil. 

5. After all these ideas, I would prune out the yellowed areas and see if it comes back. Here's an article about dieffenbachia care:

How to Grow and Care for Dieffenbachia



Hello! Unless you see active pests on your plant, you do not need to use neem oil. Look for small black dots, small white flying insects, etc. to see if you have pests. Neem oil is only for pests and will not help browning of the leaves. Good luck!