How much stuff do you need for 2,5 months traveling?
I would say not more than traveling for 4 days because you can wash and nowadays you get everything everywhere especially when you are traveling to North America. But if you wanna rent a car for a longer period than 4 days the renting of car seats for the kids gets quite expansive. Also the kids (and the parents) do not know how the car seats work, how to fix them and of course they would be worser then any car seat your kid has ever seen. For our trip during our first parental leave with our second child to Portugal (February 2019) we also took our own car seats with us. We bought a new car seat which you can take to the airplane for our older son. But car seats are big, heavy to carry and bulky. Although we had a bag which you could carry as backpack it was not very comfortable and it was almost impossible to carry as well a child if necessary. For our younger boy we already have a travel approved combination (Babyzen YoYo with adapter for a Kiddy car seat which we are using since our first parental leave June/ July 2017 with our first child in Finland).
Although you have the combination of alle the luggage not for the whole time you still have to be prepared in case you need all your hands. This happened to us in the Alfama from Lissabon where no taxi can drive you directly to the apartment we rented because it has a lot of stairs. Back then we didn’t have the solution we now thought of:
First we tried to mount the car seat of our first born to a trolly which seems to be ok but not that stable. Also you have to detach the car seat every time you wanna access the trolly. That looks like this:
And now our new solution with the already approved solution of Babyzen YoYo with adapters for the car seat + the board where we placed and fixed the second car seat (which was in the black bag/ rucksack during Portugal)