Based on what our friend Google tells me, these are the ONE-WAY metrics (of course you did both ways I'm assuming!) of the three hikes you and your friends have done :
Snowdon Miner's Track: 5.5 km, 725 meters ascent (3.4 miles, 2400 feet ascent)
Scaffel Pike Corridor Route: 7.8 km, 975 meters ascent (4.7 miles, 3200 feet ascent)
Ben Nevis Tourist Route: 6.85 km, 1324 meters ascent (4.25 miles, 4320 feet ascent)
I may have the distance incorrect; perhaps the various sites are quoting one way vs round trip distances? That could very well be. Looking at the Ben Nevis Tourist Route, this is described as the easiest way up. And 1000 vertical feet of ascent per mile of distance is VERY steep. If so, double the distances I mention above.
If this is correct, these are some quite challenging hikes! And it looks like there are scree fields and, with at least one, some boulder scrambling. I have not done the Aletsch Panoramaweg. I have a problem with exposure and that bridge would kill me (likely literally!) But based on the description it should be a fine 2 day hike for you and your travel mates. Assuming my numbers about the hikes you have done are correct.
I have another idea for you if you want an area that is gorgeous yet not quite as strenuous. Downside is there will be more tourists.
Day 1: Lauterbrunnen to Lobhornhütte then down to Grütschalp. Accomodation: take the gondola from Grütschalp down to Lauterbrunnen and stay at Valley Hostel or Camping Jungfrau (the latter has dormitories, cabins, etc not just tents).
Day 2: Lauterbrunnen to Kleine Scheidegg via Wengen, then on up to Männlichen. Stay overnight up top or gondola/train back down to valley floor to stay same place you stayed Night 1.
This gets you outrageously stunning views on both sides of the Lauterbrunnen Valley, which I find to be the most gorgeous spot in the country. You can get an idea of both of these (although not the exact routing I recommend here) in the PDF file up on this site. Look in "Moderate to Challenging Hikes" section. Lauterbrunnen to Lobhornhütte, Return via Grütschalp, and Wengen to Kleine Scheidegg.
The other advantage to this routing is, if you get bad weather, you are sorta stuck out on the Panoramaweg 2 day outing. If you get bad weather with a Lauterbrunnen Valley base there is only about 1,000 other things to do.