Hi there, I know its a long time since you asked the question, but I thought I'd answer it as it came up at my table recently. The description of Broodmaster under the heading "Eidolon Brood" states "Regardless of the number of eidolons in the brood, each eidolon has the same base attack bonus and base saving throw bonuses, but the rest of the eidolons’ base statistics must be divided between the eidolons". In the main Summoner rules, the table setting out the special abilities such as "evasion" and "ability score increase" is entitled "Eidolon Base Statistics". RAW therefore requires that all the special abilities be divided between the eidolons in the brood. As the other base statistics (such as skill points, etc) can be divided however you please based on the description under the heading "Eidolon Brood", it follows that the special abilities can also be divided however you please, so you could give the "ability score increase" or "evasion" to a 1HD eidolon. Of course the other point to note (and I suspect many people miss this) is that only one of the eidolons can have darkvision, the summoner has a "link" with only one eidolon (and presumably therefore, the others can use magic item slots which the summoner is already using) and finally, only one eidolon can "share spells". Hope that helps.