In Product page, Click on Combo Pack so Your Product will be Combo. After Click, under the Sale page there is field which is Combo pack which contain multiple Product which yiu want to add this Combo.

Also this product is stockable so will maintain the stock or product pack as well as products in the products pack

Before

After

Now You can see the Combo Pack in the POS Screen with Watermark of Combo pack. Also see in left bar with it's Available items in Combo.

In Point of Sale menu under the Configuration, Click on Show Stock Qty in Screen?. Now Your Product Stock will Appear in POS Screen.

Now You can see the Available Qty of Every Product in POS Screen. If Qty is Available for Particular Product then it Shows in Green otherwise Red.