Get the Mollys into their own tank with AQ salt and Prime water conditioner (to detoxify ammonia) and do frequent water changes. No fish should die during a fish-in cycle. You need a liquid test kit to find out your ammonia level and your nitrite when it shows up. To do that, get one of these: [ame="http://www.amazon.com/API-Freshwater-Master-Test-Kit/dp/B000255NCI/ref=sr_1_1?ie=UTF8&qid=1379681456&sr=8-1&keywords=API+freshwater"]Amazon.com: API Freshwater Master Test Kit: Pet Supplies[/ame]
Read the cycling stickies at the top of the Bowls and Habitat section of this forum. Use Prime to detoxify ammonia. Please, do not think of fish as disposable ammonia machines.
As for stocking, Molly, Betta and Guppy all require different water parameters. Research their requirements and decide what you're going to keep.
Last edited by Hallyx; 09-20-2013 at 08:56 AM.