Installing air conditioning supply
You don't say what voltage your country uses, but given that you're working in mm\$^2\$, using air conditioning, you wear sunglasses and your name I'd say you live in a country in Europe where people eat a lot of pasta! That would make your supply 230 V.


  I want to install two 5 kW inverter air cons and reading the specifications I'm a bit confused. The rated power input is 1.22 kW each.


It is not clear from your question but I suspect that 5 kW is the thermal (heat pumping capability) rating. To pump 5 kW will use 1.22 kW of electrical input. This implies a COP (coefficient of performance) of \$ \frac {5}{1.22} = 4 \$ which is good. For every 1 kW of electrical input it should pump 4 kW of heat.

From \$ P = VI \$ we can calculate that the current, \$I\$ will be \$\frac {P}{V} = \frac {1.22}{230} = 5~A \$. Actual amps might be a little higher due to power factor &lt; 1.


  I was thinking to run a 2.5 sq mm power line and use a 16 A RCD to supply BOTH outdoor units.


That should be more than enough.


  Then I read on the outdoor unit tag that the input is 1.22A but max current is 13.5 A? Does it mean that at full load they can draw up to max current for some period?


That sounds like a cautious motor starting surge. If both units were to start simultaneously it might trip a 16 A breaker. These come in various time delays, A, B, C and D. I think type 'C' is what you require. Check this with someone who knows.


  I will run them together to cool 2 large interconnected areas at the same time, never independently. If so I will need two separate lines with a 16 A RCD each or should I go from the input data for my calculations and stick with one line for both?


Again, I think one line will be OK.