Thank you for both your replies. I have been separating them as I have done lots of reading and it seems to suggest to do several bonding sessions increasing the time together and also starting with a really small area in an unfamiliar space and then increase the space each time. The first time they were together for 15 minutes then the 2nd time 20 minutes. Do you think I should be just putting them together then ? Still in an unfamiliar space ? How will I know that they are ready to go back together full time?
Its really what you find more comfortable. Bonding is definitely an individual thing and each person finds their own technique that they are most comfortable with.
Some people swear by "dating" techniques, others swear by just putting them together and keeping them together. You may benefit for trying them for an hour, then seeing how they go if you're uncomfortable jumping in at the deep end. At least then if after an hour you feel they're getting stressed you can put them back in their respected cages.
It'll always be done in your neutral/unfamiliar place, until a bond is established.
Amount of space available is also another thing suited to each individual bonder. I done bonding with approx 25sqft which gave me enough room to sit in with them and intervene if needed. Because the bonding had to be done for a long time they then got moved into another neuteral room in a large dog crate (approx 15sqft) so I was able to sleep in my bed and get up in the night if needed. When they were moved back into their shared accommodation once their bond was established, we started with approx 25sqft of room and gradually increased it over time, if any arguments broke out the space got reduced again until they were settled again.
You'll normally know by seeing mutual grooming, laying together, "bunny flops", generally relaxed behaviour.
Things like fur pulling, humping and nipping/chasing should also be non-existent or at least rare. (Both my females still have the odd chasing, humping & fur pulling but they're most definitely bonded)
ETA: I forgot to add, that moving their environment can also cause them to need to re-establish their hierarchy and is normal. It doesn't mean the bond is broken.