Check if multiple signatures match a specifc public key
I believe it could work with a RedeemScript like this (haven't tested the scripts):  

OP_IF
  3 &lt;pub_A&gt;&lt;pub_B&gt;&lt;pub_C&gt; 3 OP_CheckMultiSig
OP_ELSE
  1 &lt;pub_A&gt;&lt;pub_B&gt;&lt;pub_C&gt; 3 OP_CheckMultiSigVerify
  4 &lt;pub_S1&gt;&lt;pub_S2&gt;&lt;pub_S3&gt;&lt;pub_S4&gt;&lt;pub_S5&gt; 5 OP_CheckMultiSig


Explanation: The redeem script has two parts:
- OP_IF: this part could be removed, it is there to allow the "leaders" to spend the funds without needing the "shareholders" signatures. Depending on the purpose it could be removed (remove first 3 lines of RedeemScript and signature doesn't require OP_TRUE/OP_FALSE in it).
- OP_ELSE: this provides what you need with 2 multi-signature operations. The first one requires at least one signature out of 3 "leaders" signatures and performs a OP_CheckMultiSigVerify (there is no true/false remaining on the stack after the execution) and the second one requires 4 of 5 signatures from "shareholders".  

To spend, either one of these signature scripts should be provided (OP_0 is mandatory due to the bug in CheckMultiSig OPs):

OP_0 &lt;sig_A&gt;&lt;sig_B&gt;&lt;sig_C&gt; OP_TRUE &lt;RedeemScript&gt;


or

OP_0 &lt;sig_S1&gt;&lt;sig_S2&gt;&lt;sig_S4&gt;&lt;sig_S5&gt; OP_0 &lt;sig_A or B or C&gt; OP_FALSE &lt;RedeemScript&gt;