Partnerships are typically set up with a Partnership Agreement, which may cover some of the following shown at this website.
http://www.businesslegal.ltd.uk/blco/faq/llpfa q/purpose_partnership_agreement.htm
Does yours?
If there isn't an agreement to cover such things, there is pretty wide organisational flexibility about what individual partners can do.
The JVs I've seen before are set-up as a separate legal entities from any of the contributing organisations - this allows different contributors to have different sizes of stake (and in many cases there are more than 2 contributors). I suspect this isn't what you have here - it sounds like this is more of a formal agreement to joint development of something. Does the agreement detail what each party will input and what each party takes in output?
Can't comment on what action you can take against your fellow partners, sorry. BM