The Sixt rental location in Bern is a couple of kilometers from the Bahnhof; tram/bus stops noted below.
Depending on your logistical arrangements, particularly, where your hotel in Bern is, you could take a bus, tram or taxi. Swiss taxis are quite expensive by US standards, but the convenience may be worth it.
Even an SUV rental in Switzerland quite possibly, even likely, will not have room for luggage for 5 people staying for a week. Assuming that you do not get to Bern from Maastricht after 1900, and if I were doing it myself, my strong preference would be to drop my heavy luggage at the Left Luggage Office in Bern Main station :
or else hope for luggage lockers ( available pretty much around the clock; heavily used in August.).
I 'd carry a small bag with one night's essentials to my hotel and to the Sixt in the AM. Personally, I'd use public transport. but I am familiar with it. Your hotel might have advice, or you may not need transport if you are staying near the main station.
Many Swiss hotels are not air conditioned.
Then, when leaving Bern no later than 1900 on the way to Thun, I'd pick up my bags. The storage can easily cost 10 CHF per bag, not cheap, but maneuvering around Bern with luggage is no fun.
The alternative of three of taxi rides would probably be cheaper than left luggage fees for 5 people, but not for two people..
It is possible to ship your luggage to Thun ahead of you, but the constraint would be pick up time (open hours of the luggage office in the evening are not late) at Thun. For a fee, they have fast services and can even deliver to your hotel, but it could get rather expensive.
The SBB web site explains all the luggage services.
I'd definitely not plan to get around Bern any more than absolutel necessary in your rental. All major Swiss cities are doing their best to make auto traffic inconvenient, and provide excellent public transport.
The neat square city grid with numbered streets that you find in Omaha does not exist in most Swiss cities. Certainly, not in Bern.
Ir has been several years since i rented from Sixt. They used to be significantly more expensive tan renting from Avis. I have locked in on Avis to get the better service that they give to a preferred customer, so I really don't check costs anymore.
The Avis location is about 500 meters closer to the main station than Sixt, in the same part of the city, and is directly on a major route ( Rte 10) to the southern Emmental. There is not much difference in getting to Avis or Sixt from the station, with Sixt being a bit further, but I don't know where your hotel is.
www.bern.com/en/travel -planning/arrival-transport/transportati on
has a link to a PDF of the us routes
mapsearch.CH can be set to show bus/tram stops.
Bus stop or tram stop Sulgenau is 100 metes from the Avis location. Sixt is a similar distance from bus/tram stops Schönegg and Wander. All three stops are on line #9.
Stop Sulgenau and Wander are also on line #19.