Is my hamster's CritterTrail cage big enough if I connect two?

I recommend choosing the larger cage for sweet pea. Hamsters like to have separate bathroom / toilet areas well away from their bedding, so the one with the biggest base area is the best. Height of cage is less important. Also provide safe chewing sticks for her to gnaw her teeth on.

This cage is much better than a rabbit cage but I feel like it is too small for two guinea pigs. Have you considered making your own cage? There are many websites dedicated to this. ( https://abyssinianguineapigtips.com/make-guinea-pig-cage/ ) ( https://diyprojects.com/diy-guinea-pig-cage-ideas/ )

If the cage is cleaned frequently the ventilation may be adequate however I would be very nervous that the hamster would escape from these open areas. They can be very agile climbers and are escape artists. I would recommend a commercially available cage instead to ensure that your hamster does not escape! Also, even if you place a mesh over the area, if the hamster can get to the corner/edge of the plastic they can easily chew the plastic and escape that way!

Do not use an aquarium tank. A suitably sized (and secure) wire cage with a solid bottom is recommended. HabiTrail and Kaytee have excellent choices for cages. Buy the largest cage you can afford and fit in the chosen space. You can use recycled paper bedding such as CareFresh or Yesterday's News. Aspen shavings or pellets are also acceptable. Do not use pine or cedar shavings as these can be irritating. A commercial diet from Kaytee or VitaKraft can be fed from a ceramic bowl. A ceramic bowl prevents gnawing and tipping. A non chewable water bottle can be hung to provide fresh water daily. Other necessary items include chew toys and an exercise wheel. Find a veterinarian experienced in treating pocket pets and have your new addition examined to confirm good health. Feed, water and exercise daily. Clean the cage weekly. These little guys require very little care and can provide lots of entertainment. Congrats and enjoy!

I'm sorry but your photos did not come through. But, I can tell you that for one guinea pig the recommended hutch dimensions are: 7.5 square feet cage (minimum), but more is better; generally 30" x 36" is a good size.

The size is not so important. It is important not to move the toys, housing, etc around too much, ie put them back exactly where they were after cleaning out the cage, so your hamster can find his way around, knows where to hide quickly and does not get stressed. Make sure you do not startle him when trying to pick him up. You may want to make the same noise before picking him up. He will learn quickly then, that this is you and not be scared.

Yes, these can make great homes for hamsters. Be sure to secure the top to prevent escape. Be careful to allow adequate air circulation. You can make use of the vertical space as well. Do not use colored plastic bins.