you can never 'combine' two itineraries into one. So the answer is no. Though the agent at check in should be able to check your bag through all the way. To do this, don't use the kiosk, ask for an agent, and make sure you have a copy of both tickets printed for this. Also, expect this to take extra time, so arrive at the airport earlier than you normally would.

Also, since you are on two separate tickets, give yourself plenty of time to 'connect' (I use quotes because it's not actually a connection). If your inbound flight is delayed, and you miss the flight to TLV, UA can simply call you a no-show and cancel your itinerary. Many have found UA will protect them on the next available flight, but they are in no way required to. If it's important to travel with your group, especially, this advice goes triple. I would say you should plan to arrive in EWR mid-afternoon to give yourself plenty of time of things go wrong. If it were me, I might even try to arrive sometime in mid-late morning, plan to make a day of it in NYC (NJT can get you to Penn Station and back in 30-40 mins) before you go to TLV.