Well if your responsible enough to take care of all of the other animals.. I don't see how adding one guinea pig would hurt. Ive owned two guinea pigs and I can say that they are very cute, require minimum care, and they don't smell. As long as you give them enough food and water to last the whole day (if your gone the whole day like you say you are) then they will be able to take care of themselves.
Guinea pigs don't smell, but their cages might smell if not cleaned from time to time. Ive never had an odor issue from my guinea pigs.. if the room smelled like anything it would have been wood chips.. cause thats what I used. Im sure pet stores now sell the odorless stuff that can be used for guinea pigs.
To tell you the truth.. guinea pigs do kinda act like they are dead.. they don't move much.. so you should get two to keep each other company : they are quite friendly but can be really frightened, mine have never bit me.. So in the end, I say getting one wouldnt be a bad idea, they make great pets : I hope this helped.
It sounds like you already have more than plenty of pets on your hands. Guinea pigs are awesome and they don't just sit there and play dead, but they require responsibility and when you already have 22 pets to take care of it becomes hard. You couldn't forget a couple days (well you could but your guinea pig would be miserable, hungry, and thirsty) and also, having several cats and dogs around could make it dangerous, they could easily hurt your guinea pig.
Your parents are right, as awesome as guinea pigs are, they do smell unless you clean their cages daily. As it is, their cages need to be cleaned twice a week. There are many other specific needs for a guinea pig and you should research them.
They are not harmful, they only bite if you make them mad or irritated. And guinea pigs are social animals that get lonely if not kept in a pair or trio of the same gender. Their bodies can't produce vitamin C so they need FRESH (emphasize that word) vegetables every day.
This isn't all, so do some more research before getting some. Hope this helps.
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