Yes, when adult they won't moult anymore .. If you've had your male for 2 years and he hasn't moulted in that time and the 2 you have just brought are larger than him then that sounds to me as if they should all be adult. Can you post some clear close pictures of them?
If the 2 larger scorps are females i'd set them up in each their enclosure and just let the male cohabit with one of them, or (more likely), i'd let him have a bit of quality time with them both now and again..........In my opinion though, a communal setup consisting of 2 females and 1 male is just asking for trouble....you could quite easily lose one of the females or your male....A more common 1.1 or 2.1 setup though is usually much less problematic.....The groundplan size of your proposed enclosure sounds just about right......although.......LQ's will burrow if given the correct conditions so if you'd like to let your's burrow you'll also want room in that enclosure for a 5 to 7 inch depth of consolidated sand with that bringing the surface of the substrate to close to the top of the enclosure.
You can read all over the place that they should be kept on sand with stone/dry grass/dry detritus furniture but if given the chance to burrow they will do so. If just kept on sand all they will be able to do is dig scrapes under surface objects but if given the preference, as in an enclosure with half sand, half consolidated sand with depth.....then yeps, you'll always find they'll rather live in a burrow than under a stone.
Keep them between 85-92F with a drop down to 75-80F at night and no water bottle. These guys will get all their moisture from the prey they catch so no need to dampen corners either...A very occasional fine misting representing a rare morning dew (not to many of them throughout their distribution range!) might be ok though.
Here's a couple of pics..The first showing an adult male L.q hebreus....These are very slightly smaller than normal Lq's so bear that in mind when comparing yours to it....The point though, this one is adult..7 instar.
And here's a pic of an old lq setup.....The scorps (1.1) dug a burrow down through the consolidated side and spent most of their time in that. At night time they are all over the place but never once were they found hiding under the stone on the loose sand.
