Okay great, thanks for your reply Allison & Canooknic.
the important is to show that u have a joint account; there's no need of statements if u have the initial letter from the bank, with both names and the date clear; also u can scan the bank cards and wipe out the middle digits for security (usually the cards from the same account have the first digits in common, and the same expiry date); but if u don't have lot of common law proofs and u used that account a lot for ur expenses u could also show statements - emphasize share expenses, how u pay the rent and utilities from that joint account, how u buy important things for the home from there - furniture, fridge, washing machine, etc......of course, if u don't use it there's not really good idea to show blank statements (u don't want them to think that u opened the account just for the sake of the proof for them) good luck!!