I have continued to read about MOSFETs and thermal design and it seems to me that any calculation that would actually tell me anything valid is way over my head, I would love to be able to simulate my board with some thermal simulation software but 1, I don't have one and can't afford to buy one, and 2, I am not sure I would be capable to collect all the necessary information needed for something like that.
Some documents give a perspective that says that I can't really find out anything without implementing a prototype, though I wasn't really looking for answer for at what temperature my circuit will run. I think I was simply trying to figure out if doubling the number of MOSFETs would be beneficial.
Assuming(no matter if it is true or not) that switching losses doesn't heat the MOSFETs enough to be considered I think that what Klaus writes make sense, after all the resistance of 2 identical MOSFETs is half of the resistance of 1 such MOSFET. If one would compare two situations in which situation 1(#1) has a single MOSFET with 2mΩ RDS(on) and situation 2(#2) has 2 MOSFETs with a combined RDS(on) of 2mΩ then I could imagine that mtwieg would be correct.
But in this situation it would be the case of halving the RDS(on) from approximately 1,43mΩ to 0,715mΩ, I don't think that this is really necessary for my circuit to work so I will let it be decided by the board layout. If I have space enough to use 2 parallel MOSFETs in my synchronous buck converter then I will use parallel MOSFETs because it might very well make other things easier due to a decrease in the temperature variations of the board.