Multitude of Issues Not sure where to start

[Nharmswhey]

This is my first post on here and i hope that im in the correct spot. We bought our house last year and the pool was already up and running. we paid someone to close it but i chose to open it. I have an 18x40 in ground vinyl lined pool. It has a sand filter on it and 3 jandy valves with a 2 hp pump. 1 jandy valve for each skimmer and 1 valve for the main drains on the bottom. I just opened the pool last weekend. I have noticed a crack in the manual air release on the sand filter and replaced it. I have a serious lack of suction from the skimmers and when i turn both skimmers on and the bottom main drain the pump immediately runs dry. As soon as i turn one off everything fills back up. I have noticed when this happens the pump also gets very hot to the touch. Not sure if its related or not. And last but not least im constantly having to release air from the top of the sand filter. Any help would be great as im not sure where to start.

[Denniswiseman]

Only have one line open at a time to determine where the air leak is
Also silicone grease the pump pre-filter "O" ring on the lid

[Nharmswhey]

I have greased the o ring and it has stopped the air leak from the top of the sand filter. I have ran each line individually. The skimmers had 18 psi each individually, when ran together there was only 12 psi . The slide had 30 psi individually. and the main drains 18 psi when ran by themselves. With the 2 skimmers and main drains on at the same time it evacuates the water from the pump sight window and sucks air in the the 6 way valve.

[Denniswiseman]

When you vacuum does air collect in the pump pre-filter? as this is what happens when the pump is put under load, like when you have all lines open
Have you tried partially closing the jandy valves to restrict the load
Another thing to check is the pump drain-off plugs
Your slide wouldn't be on the suction side but on the returns