Eurail Pass?

Yes, they are all covered. Is it a good idea - probably not.

But, tickets in Italy are relatively cheap. In Italy it is usually a lot cheaper to buy normal tickets than to get a pass. Tickets are even cheaper if bought in advance. Go to the Italian Railways site ( http://www.trenitalia.com/tcom-en ) and price each of your trips in Italy. Go for a date 1-2 months in advance so you can see the cheapest tickets, which sell out nearer the date. For example Venice to Milan ("Venezia S. Lucia" to "Milano Centrale") from €19.90!
When you buy a ticket in advance, it is for one specific train (same as air tickets are).

For Switzerland, a Swiss Pass is better value than a Eurail Pass. The Swiss Pass covers more trains, buses and boats.
For detail see here: https://www.sbb.ch/en/leisure-holidays/travel-in-switzerland/international-guests/swiss-travel-pass.html
Also consider the Swiss Half Price card. Details here: https://www.sbb.ch/en/leisure-holidays/travel-in-switzerland/international-guests/swiss-halffare-card.html
Sorry, you have to do the arithmetic yourself to work out which is cheaper!
For a map to show what these pases cover, see here: https://www.sbb.ch/content/dam/sbb/de/infotexte/uebersichtskarte-sts.pdf

Minor points:

• "if multiple legs occur in a day, does it matter?". No, with a pass you can take as many trains in the one day as you like. It is normal for train journeys (unlike air) to require multiple trains. The system is designed as a connecting network.
• "Tirano to Lake Como" "Lake Como to Venice" - Lake Como is not a place, it is a big lake. You need to decide where on lake Como you wish to visit, then look up transport to and from that place. There is a rail line down the east side of the lake that runs from Tirano to Milan.
• "The Bernina Express offers a purchase to add to this which is great!" - Note that the Bernina Exptress is an extra tourist train. You are paying extra just for this train. The Bernina line (like all other rail lines in Switzerland) has one train per hour, for which you do not have to pay extra and you see the exact same mountains.

I do not think a Eurail pass will be of benefit to you for the trip you have outlined. The 8-day 2-country Select Pass would be $800 for two ( Saver rate), or $400 per person. You are only using it seven days, so each day's use will cost $57. Only one of your Travel legs is more than that; the others are less, often much less is you just buy tickets ( sometimes in advance as explained below).

First, I suggest you make your overnight or multinight stops in Luzern, Pontresina ( instead of Chur), Varenna on Lake Como ( instead of Tirano), Venice ( multiple nights), and Milan (one night before catching the train back to Zurich for your flight). This is the exact path we took two years ago and it breaks up the journey well, with overnights in nice scenic villages like Varenna and Pontresina. We actually stayed overnight in Samedan nearby, and you could too.

You can find the costs for this trip on SBB.ch.

Zurich to Luzern, 26 CHF.

Luzern to Pontresina, 94 CHF. This is the one expensive journey.

Pontresina to Varenna, around €20-35. This is where you can get a good discount by buying in advance, as it is a cross border journey. We only paid 32 CHF for both of us on this segment, but we took a regular regional train, not the dedicated BerninaExpress. Same track, same scenery, without the panoramic cars.

Varenna to Milan to Venice, around €25-35. Again, this is one where you can get significant savings by buying in advance, this one on Trenitalia. As. Bristol noted above, Economy tickets on the fast Milan to Venice train start at €19. Add €6-10 for the regional train from Varenna to Milan (a one-hour journey).

Venice back to Milan, another €19.

Milan to Zurich, 34 CHF if you buy several months in advance. I just checked this today. The regular fare is 88 CHF, so this is a significant savings. ( Ten years ago we saved almost $500 by buying these advance tickets for four people traveling Zurich to Milan round trip). This is a direct train and spends much of the time in a tunnel, so not all that scenic, but it is fast and inexpensive.

This plan brings the number of travel days down to six instead of seven, making an 8-day Eurail Pass even less desireable.

One important point to note with Railpasses is that these do not include the seat reservation which are compulsory on the Italian express trains. You'd have to pay separately for those. Even with a Railpass, if you're caught without a valid reservation for the train you're riding on, you'll face hefty fines (~€50 PP) which will be collected on the spot!

A Eurail Pass may work for you under the following conditions,
1. Get a 6-day pass.
2. You buy before the end of this year to get the 20% discount.
3. You are 27 or under so you get the youth price.

The leg from Chur to Varenna-Esino can be done in one day if you take the morning Bernina Express. Nothing much in Tirano, and it is only another hour and 30 minutes to Varenna on Lake Como. Even if you did stay over in Tirano, the train tickets from there to Varenna are only 7.30 EUR per person. No point in adding extra pass days for cheap tickets.

You will have to buy seat reservations for 10 EUR per person for the Milan to Venice and return trains. Not sure about the cost of reservations on the Milan-Zurich train. It is an EC train and seat reservations are required, at least for the Italian portion.

It does not look like you have enough travel cost in Switzerland to justify Half Fare Cards or Swiss Travel Passes. The cost would be more than the cost of just buying tickets as you go.

Good catch, Sam. That brings the cost down to $264-276 per person ( depending on age), plus the cost of seat reservations for the Frecce trains in Italy and the BEX in Switzerland.

If you're visiting Mt. Pilatus from Lucerne, either pass covers trains and lifts uphill as far as Kriens/Alpnachstad, then 50 percent off above Kriens/Alpnachstad. The Select pass gives 50% off lake boats while the Swiss Travel Pass fully covers them. The Select pass offers those 50% discounts in between the counted rail travel days, while a flexi-day version of a Swiss Travel Pass does not (but with a consecutive-day version, you're not really counting).

The Italian portion of your trip is quite short and cheap. On the return to Zurich, a Swiss Travel Pass would kick in from Chiasso (the usual route) or Domodossola, so you could buy a (reserved) Italian ticket just that far.