I have limited practical experience which i try to compensate with a ton of reading.
From the pics and from your descriptions it sounds to me that you have actually no problem at all.
Look at the way they r resting. They are also comfortable enough to eat next to each other.
A bit of rough and tumble as well as chasing each other is simply normal.
hissing? take it this way, they are likely to be teaching each other the limits that they do not like to be crossed as well as they are telling each other "this hurts", "that I do not like" and so on.
also keep in mind that they are establishing hierarchies as well as their own private territories.
We experienced the same the first time we introduced a new cat to our resident cat, the guest cat staied with us for a week or so and even when they were best buddies after the first few days they wold still have the occasional hiss.
since 2 weeks we have introduced a new kitten (4 months old) to our older cat (2 years old) and only now the older cat seems to start "tollerating" the new comer.
So no worries for you, u r doing great and fast. I have heard of cats who tool up to 6 months before actually tolerating each other.
Just keep doing what u r doing as it seems to me to be working fine for your 2 new jewels.