Moel Siabod has excellent views in almost all directions. You can see just about every mountain group in North/Mid Wales from the summit. You could do a two day trip starting at Capel and walk over towards Cnicht and down to to Beddgelert.
There are lots of little lakes between Siabod and Cnicht, which are ideal for water/camping.
The east ridge is straightforward. There is an easy scramble up a gully at the start. There are several nice spots to cam on the summits, especially between Llewelyn and Craig yr Ysfa. However, there is no reliable water source on the tops, so you will need to carry your own up with you.
The ridge is an excellent sport for sunrise photos. Less so for sunset, as at this time of year the sun just disappears behind Llewelyn.
It sounds as though your children should be fine, but only you know their capabilities. N Ridge of Tryfan is pretty easy and most difficulties can be avoided by easier alternatives. I took my children up the N Ridge when they were about that age.
Also you have to make sure they do what they are told. I took my children and a cousin up one of the routes on Little Tryfan (about Diff) at about the same time. We were roped and it started to pee down. We got to the big ledge at the top and cousin was told to sit and wait and on no account to try and climb the greasy wall above the ledge. Of course he did and promptly fell off. Luckily he didn't bounce off the ledge and go down the big drop below it. So I no longer take anyone else other than my own children up any sort of scramble/climb.
I have an MSR set of pans, which I think is stainless steel. However, almost all of my trips are now one or two nights and I use freeze dried food. Hence I only need to boil water rather than cook, so I got an Alpkit titanium pot. I use one of their long handled spoons, which can reach right to the bottom of a food pack without getting your fingers inside it.
At one time (70's and 80's) Mountain Goat ran a mini bus service to Wasdale. However, it looks as though they only do tours nowadays. It's a shame nobody else has taken up the idea of running a mini bus service to Wasdale Head.