Animated Knives and Cleavers (animated object), Diminutive

HD: 4d10
AC: 18 (+4 Dex, +4 Size)
Speed: 0 ft / 40 ft fly
BAB: +3
Grapple: -9

Str: 18
Dex: 19
Con: -
Wis: 1
Int: -
Cha: 1

Fort: +1
Will: -4
Ref: +5

Attack: Slash +7 1d2+4 or Peirce +7 1d2+4

I need to give it 2 feats and it has 14 skill points to spend.

I also would like to require a reflex check to grapple the knives and cleavers, of DC 15, since they are so small and quick. Is there a way to that within the established rules? Is this fair to my PCs

I'm aiming to pit 5-8 of these against a group of 5 level 4 PCs with the hopes that they will lock them in cabinets or drawers as an alternative to a strait fight.