Is it safe to use cat or ferret shampoo for bathing my rabbit?

If the bunny seems ok/is behaving normally today (normal appetite/energy/breathing) I wouldn't be worried about toxic effects but skin irritation could result if the wash was very perfumed. If the bunny wasn't too stressed by the bathing you could try washing her with a puppy/kitten shampoo from the pet store to remove any of the remnants of the body wash.

Bathing can be quite stressful for rabbits. Their fur can take a very long time to dry which can lead to low body temperature. The stress can cause a degree of shock but seizures are unlikely unless there is an underlying medical condition. The best course of action would be to use plain, unscented baby wipes or pet wipes to clean the soiled areas. If necessary, spot clean her using warm water and dry her thoroughly to prevent chill.

In general, ferrets do not require bathing unless they have gotten into something out of the ordinary. If you are going to bathe them naturally, I would use a 1:1:1: mixture of oatmeal, warm water, and baking soda.

There are cat and dog specific shampoos available at most pet stores, or on big box websites like Chewy or Amazon. While you certainly can bathe your kitty, I typically don't recommend this as a regular activity since the majority of cats do a great job of cleaning themselves. Unless your cat is getting herself into something that is causing her to be overly filthy, I would recommend letting her do the job herself to avoid yourself getting battle wounds. Hope this makes sense.

It should be fine. You can moisten a cotton ball and dab the ear tip then monitor for any reaction. If you see none, gently clean the ears. Nolvasan Otic and EpiOtic are also acceptable ear cleaners. Use only cotton balls, not cotton swabs to clean just what you can see and reach with a finger.

I would be careful using products designed for other pets on your rabbit as they can become very easily injured. If you'd like Lennon and Waffle to go outside or have more room to run around, an X-pen or other playpen type structure can help to keep them contained while allowing them to stretch their legs and get some fresh air. As for groooming, daily brushing of longer haired breeds can help keep the coat shiny, remove excess hair, and help prevent mats.

I would never use essential oils directly on your rabbit. Frankly, the best way to help with the odor is to keep your rabbit and his housing very clean by frequently changing litter and bedding. And never bathe a rabbit unless he has soiled himself and/or is very dirty. They usually groom enough to keep themselves clean. Rabbits are very delicate and sensitive which is why they are often used as a human analog in product testing.