Can I add an adult molly to a tank with baby albino clawed frogs?

Thanks for your questions about your fish tank. The smell may be from the strain that the extra fish are putting on the filtration system within your tank. You can try to perform a water change, however use caution as the babies are small and may be accidentally removed with the suction while you change the water. Preventing breeding in the future may be difficult, but one area that you may be able to adjust is the feeding of your fish. It is common to overfeed fish, and this can lead to breeding, obesity, and other undesired problems. A general rule of thumb is to feed fish what they can eat in the span of 10 minutes. I hope that gives you a place to start, and congratulations on the young fish!

You should use one or two small, inexpensive but hardy fish to cycle a tank. Ideally, the tank should be cycled empty to prevent fish losses. You can also use a quick start product to speed up the cycling.

The salt would probably irritate the snails. If you still have frogs in the tank, consider a salt bath instead. Dissolve 1 tablespoon of salt in 5 gallons of water then remove the frog(s) from the main tank and allow for a swim of no more than 60 seconds in the salt bath. Rinse then return them to the other tank or hospital tank.

Feeder fish can be added to the diet, however you must consider the source. Typically these fish are kept in a tank with hundreds of other fish. This predisposes them to infection and parasites which could be transmitted to your frog. As an occasional treat, they are fine. Stick with responsibly raised insects and nightcrawlers. Another treat to be given occasionally would be a pinkie (baby mouse).

Ideally, a 5 gallon tank would be better for both of them, but as long as she is a "passive" fish, an ADF should be fine with her. You'll need to monitor for any aggression initially because female Bettas can be just as aggressive as the males.

Mollies do come in gold or orange colorations, but it is difficult to determine from that angle. If you can repost a broadside picture in a new question, that may make identification easier. If it is an egg laying species of fish, the third image could be an egg but I have reservations saying definitively without something for scale. It looks too large to be an egg. As an aside, if you leave the Molly fry in with adults, they will likely be eaten. You can separate the out, remove the adults, use a breeder screen or provide plenty of cover for them.

Maintain pristine water quality in the main tank and monitor the fish for similar symptoms. A bit of aquarium salt ( not table or Epsom salt) can be used as a general tonic to reduce stress, improve gill function, treat minor infection and aid in recovery. Dissolve 1 teaspoon of salt per gallon of water in a cup or two of tank water and gently pour it into the tank. Treat for no more than two weeks then perform partial water changes to decrease salinity. Use only conditioned water that is temperature matched to prevent stress or shock. I am sorry for the loss of your frog. Your remaining ADF sounds quite ill by your description. Again, maintain pristine water quality in the quarantine tank with a water temp of 78 F. ADFs, and amphibians in general, ate quite sensitive to changes in water chemistry. Elevated ammonia or nitrite levels can kill. Other possibilities for the bloating include improper diet, obstruction or kidney failure. You can try a fast for a couple days along with salt baths. This may relieve the bloating. If it is dropsy, unfortunately by the time a frog is bloated, the survival rate is very low.