Hi, We don't have bunks in our Class A and, from what I've seen of most bunk floorplans, we wouldn't want them. For several reasons.
First of all, kids will sleep anywhere. We opted for dedicated living space over dedicated sleeping space. Change-over at night-time and morning is about a 5 minute process. Less, now that they are all old enough to do it themselves. (When we got the rig the kids were 7,4,3,1.) We keep the sheets & pillows in the overhead cabinets. No big deal. Yet having those two sofas and dinette really gave us plenty of space so we could all watch a movie on a rainy day, or play games at the table.
Second, the bunks take up what would usually be closet & drawer space. With 3 kids, you'll need lots of closet space. You never have enough, but we certainly wouldn't want to give up any of what we have.
Third, and I didn't think of this until after we got the rig, is that the bunks are too close to the "mommy & daddy" space for most bunk floorplans. On our rig, the kids are sleeping up front, we have the bathroom/closets/hallway separating us with our bedroom at the end. We turn on the overhead fan (AC or heat or just fan) for some background noise and now wifey and I can watch what we want in the bedroom without worrying about any inappropriate language being heard by the "little ears". Or, should things progress and wifey is feeling a bit romantic, we know there aren't ears pressed on the other side of a paper-thin wall trying to hear what's going on. :)
Now, as to the two floorplans you mentioned.
35QBA: I don't like the bunks for the reason mentions. But, I do like the "all in one bath". In fact, with cabinets where the bunks are, this would be a very nice floorplan, in my opinion. I guess on those "amorous nights" you could always have the kids sleep up front. :) Seriously, though, I would ask Tiffin if they would replace the bunk area with closet & drawer space.
34TGA: I don't like the split bath. I believe in that floorplan, when someone is in the shower, the rig is now divided. People in the front can't get to the back, and people in the back can't get to the front. This is an OK floorplan with 2 adults where your spouse might not mind you walking through, but obviously won't work with kids. Picture this: You're all trying to get dressed to go out somewhere. All of the clothes are in the bedroom area, but if someone needs to take a shower, how will people get to their clothes? How many can you comfortably (and with modesty) fit in the bedroom to get changed together? Just something to think about.
By the way, 100% correct thinking on Tiffin. They are on the top of our list IF we ever buy another motorhome. But our dual sofa, dual slide 36' rig has been the PERFECT floorplan for us. My biggest problem with many Tiffin units is that they seem to have lots of floorplans with the split bath, and that isn't our preference.
Just out of curiosity, have you priced the 36LA? I'm not crazy about bath and a half units, but with kids, it's a nice floorplan. In my opinion, an extra bath is far more useful than bunks. But as I look at it, there is still that paper-thin wall between the living area and the bedroom area. So, I guess this one wouldn't pass our test. :)
Oh, and I would highly recommend the optional driver's side door. Very convenient.
Good Luck on your search. While Tiffin is a great company, I'd recommend Winnebago as well. Keep looking. It took over 2 years of research for us to find our ideal solution. The rig we have is our first RV and I spent lots of time soliciting opinions from the fine people on this forum to help us arrive at our final solution. It was time well-spent. :) We went from looking at small hybrids to tow behind our Honda Odyssey minivan to the 36' Class A rig towing the Odyssey, with all sorts of ideas in-between. But we ultimately arrived on what worked best for our family of 6.
Good Luck,
~Rick