I mean for multi-sig wallet it's harder to find public key if there's output transactions?
No. It's not really hard.
As mentioned by jackg, you should use the redeem script to get the public keys.
I didn't know how it can be done. I just made a search and found out it's really easy.
Click
here to see one of the transactions made from the address you referred to in the OP.
See the input with the index number 135. The sigcript includes 3 hex data. The last one is the redeem script and is as follows.
522102707f8c41a9ce80bd85c335ce37617388fe8fd5c7b6079f730fc8b7159867cb3e2102f61a255027b492203f04396474e032e759367ad32cdb1b317074e216718f9b532102ae11e6f80d33717c8dffcbd4e480b95f82f9fe7478cb166beebddd5b062c9f9653ae
For getting the public keys, all you need to do is to decode the redeem script using
coinb.in tool.
The three public keys used for generating the address in question are as follows.
02707f8c41a9ce80bd85c335ce37617388fe8fd5c7b6079f730fc8b7159867cb3e
02f61a255027b492203f04396474e032e759367ad32cdb1b317074e216718f9b53
02ae11e6f80d33717c8dffcbd4e480b95f82f9fe7478cb166beebddd5b062c9f96