The Swiss Pass is usually the most cost-effective to get around. There are hotels with triples and quads, though few and far between. Most European hotel rooms are small to begin with, and unless it's a sizable room you may find one room cramped for three. In our favorite mountain village, M rren, the Eiger Guesthouse offers excellent value for families, including 2-6 bunk dorm rooms. Very cost effective.
Every town has rooms for vacationers.
Again, the local tourist office will probably have a list. Do your own breakfast and picnic lunch, and consider cooking in for most evening meals as well if you're in an apartment. The most desirable villages in the mountains all have supermarkets in the center of town. Much the same as stores at home, yet with differences that tell you your away from home. COOP is the most often-found chain in the Berner Oberland, and Migros is a large Swiss chain found around the country.