Hi. The Shoto hilts would be a good size for your boys and even adult boys
will use them. Because these blades are heavy grade for dueling... they are weightier as the wall of the blade is thicker. There is no difference in the cost between blade sizes so I would choose the 26 inch blade for both of them or if at some time you can upgrade the length... start with the 18 inch. This means that they will be in closer vicinity to each other and the saber might be used more in jabbing like motions. Almost guaranteed not to damage your home as they swing the sabers. Some of the blade length will be lost inside the emitter.
Cutting down the blade length with a pipe cutter or a dremel is fairly easy to do and there are clear YouTube instructional videos and lots of members here to assist you. The pointed tip is rounded off smooth and under adult supervision should not be a safety concern.
Perhaps choose sabers that have a more simple design that small fingers cannot get caught on and can grip more easily. Good luck with your selections and ask as many questions that you need.
EDIT: Have looked more closely at the blade lengths/weight and I see no reason why the 26" blades would not be the most suitable choice instead of the much shorter 18". Your boys... even the 2 year old should be able to fairly quickly adapt to holding and swinging this smaller saber combination.