A stand is one model on one base, one "in game unit".
HQ's you'd need to assign as required. I suspect two for the tanks (as that's @two battalions, Israeli style), and one or two for the infantry & support weapons. Deffo two if you're using two mortars on table. Being flexible these can effectively roam wherever needed and command anyone...
With 2-3 players per side I'd probably go with two players on the Israeli side and use CO+ 1 HQ for one, and two HQ's for the other.
For the Egyptians - the Egyptians have eight "modern-ish" MBTs, so I'd group them as one unit and parcel out the rest to the infantry in dribs & drabs (I might be wrong but I think that was doctrine, the heavies and the older tanks got to play infantry support? The SU's as well, although something reminds me they might have been dedicated AT assets like the ATGW vehicles?.
So - 1 HQ - T-55 & T-62, PT-76 for recce, ZSU-23-4.
You've three infantry companies (either 3 Inf or 6 Inf plus their APCs and heavy weapons). Give each a HQ. I'd probably add a tank to each (T-34 or IS/T-10), and parcel out the ATGW and SU as well so each has something meaty. With the remaining AA assets I'd give each one a stand, assume they're a kind of a composite of the remaining weapon systems - probably give each a 57mm towed gun?
That gives you three reinforced infantry companies for holding the line, plus a tank battalion for counterattack purposes. Four HQs plus a CO should be enough for three players - each gets an infantry position, someone gets the tanks as well and they can fight over the CO