Hello And A Few Questions

Hello all just a few questions, ive found online a  compatability chart saying i could have a betta with guppies is this true?
Also my misses tank somehow keeps getting little red snails :/ how do i stop this?
Last one lol my platys tails are going funny by size like shrinking or shriveling up how do i stop this?

Hello! I'm still fairly new to fish keeping,  but think even I might manage to be of some help to you! If I am wrong someone will be by to point it out and give you the correct information.
1. a betta and guppies - this is something I looked into as bettas have a great reputation as an interactive fish but I personally chose not to risk the mix after research.  Bettas  will generally view guppies as juvenile males (whether they are male or not) due to a guppies exaggerated tail and colouring. It will try to chase them out of its territory (your tank) but as there is no escape the guppy will be hounded and attacked until it is no more. Most fish keepers don't risk it. There are however exceptions to the rule where guppies and a betta live together nicely but this all depends on the individual bettas personality. Something you cannot test while viewing them in a shop. Also, no shop I know in my area would knowingly sell a betta to live with guppies or guppies to live with a betta.
2. Snails are a common problem. They are introduced to the tank on live plants. They are usually eggs on leaves so are only visible after some time when they hatch. There are two options with snails. Either accept that they are there (most fish keepers have them at some point or another) or remove them. Removal depends upon your tank and preferences. There are fish that will happily eat snail but they require large tanks. There are chemical treatments that are easy to get hold of online or in your local fish shop. The third option is to get 'assasin' snails. These are a breed of snail that stay a good size and will eat any snail their own size or smaller. The benefit of these is that if they breed you will be able to sell them on easily. It all depends on your preferences. Snails breed readily when there is sufficient food for them - over feeding fish is the most common source of food. Different snails breed at different rates so without knowing the type it's hard to say if that's all it is.
3. Sadly this is where I am the least helpful. Do the tails look ragged and tatty? Are they bleeding or red? This could be fin rot, at which point you need to treat with medication - again readily available online or in your fish shop. You will need to treat the whole tank and quickly as this can be a big problem although it is thankfully easy to recover from if acted on in good time. Or it could be you have a fin nipper in your tank. What other fish are in there?
I hope I've been helpful, and as I said if I'm wrong someone will soon let you know!

Thankyou ive purchased fin rot treatment today theres no nipping or bleeding.
The fish i have is 2 angels, 12 platys, 3 swordtails(1male), 5 columbian tetras, 2 pictus cats, 2 upside down cats, 2 synodtis cats, 1 sailfin plec, 1 red tail shark and a ruby shark and a betta.
i have not seen any fighting and theyve been together for months except for 5 platys.
i will look into getting the snail that will get rid of the other snails thankyou for your advice

Blimey a veritable smorgasbord of fish! Ditto what Richard said!

Pandemonium has covered points 1 and 2 quite thoroughly.
I would just add that I have witnessed what a betta can do to guppies as one shop I visited had both in a tank. All the guppies had bits missing from their fins. The betta was herding them into a corner, one at a time, then pouncing.
I would avoid using a chemical to kill snails. The main cause of a lot of snails is over feeding the fish. Snails are not a bad thing in a tank, they just need to be kept under control by the amount of food going in the tank.

As for point 3, it does sound as though something is nipping the fish, and perhaps finrot has set in as a result.

Your sailfin plec is going to need a bigger tank before long, tanks of over 100 gallons (375 litres) are recommended