Playing or aggression?

Hi, I’m relatively new to owning ferrets so just need another opinion so I know I’m doing to correct thing. I have owned Frankie (the bigger one) for a while now and have for the last month been working on introducing Benny (the smaller one) into the household however I’m worried on whether this is fighting or just playing. I understand that Frankie is dooking or chirping but I’m concerned on whether I have done this too soon and benny is too small? I have been on constant look out for any blood during these 30 min daily introduction times and so far nothing but I’m scared that if it is aggression that may change. I think they are just playing due to the research I have done (which is admittedly quite a bit) but just would like a second opinion?