In my application I have this idea for a some large number of people who don't completely trust each other, endevor to buy something collectively, like a plot of land that would get subdivided into lots for themselves. 

Each of the users make a payment to the society (a n of n multisignature wallet) and in the end payments are made out of it for purchase of the common property land and then implementation of services. 


The most simple non-trivial case is a 2 of 2.  Let's make up two users Alice and Bob.  Can I create a payment transaction from both Alice and Bob, so that both of them pay 0.1 mBTC for the society payment but if unless both sign (pay) then neither pays into it?  Is there a wallet that does this kind of thing already?

I think this could be a good way to prevent people from running away with funds.  I think the upper limit for n is 15 in Bitcoin.  I have a copy of the private keys for some test wallets.  Send me a private message if you wish to participate in trying to do this.  We should only use popular clients like Electrum, core or Armory.  I don't think I should be writing custom wallet software!

Perhaps this can be done with the CSV import mechanism in Electrum.  Maybe there is something we can use from the RPC of one of these clients.