Is splitting AES ecrypted data safe? Say I have a key, an iv and an AES/GCM/NoPadding encoded string and I want to split this information between three people such that only jointly can they reveal the secret.  

Is it safe to just split all this data to three equal chunks and provide to each party in a format "1/3 of key-1/3 of pass-1/3 of iv"? Under "safe" I mean, is it possible to come up with some kind of efficient attack while having 1/3 (or 2/3) of all the data?
Just use Shamir's Secret sharing: wiki link

It's designed by Adi Shamir, who is the "S" in RSA. It's fairly simple to use and there are no known weaknesses in it. While it doesn't split the data, splitting the key may work just as well (unless you absolutely must split the data.)