To be honest I didn't drive with my first and the carry type seats are a million times more practical than the ones which last until age 4.
I know that seems practical, but realistically the worst/most inconvenient stage of car seat for non drivers is the in between one, the "Group 1" or large, fixed in place toddler seat with a harness.
Infant carriers with a handle and (especially) which are compatible with a pushchair are a doddle to deal with, as are high backed boosters if you get a basic one.
So realistically I'd be looking at maximising the time you're using those seats and minimising the use of the toddler one. That means getting a large infant carrier either without a height limit (e.g. Maxi Cosi Cabriofix, Joie Gemm/Juva) or one with a long height limit on it (e.g. Cybex Aton M, Britax Babysafe i-size).
They all say they're compatible up to about a year, but if you don't use the car a lot and you really want to, you can absolutely stretch this out by using the seat right up to its very limit (which is 13kg or the baby's head is level with the end of the seat, or the height limit if it has one, whichever comes first). If you end up with a large baby and have a decent sized seat, this will be about 18 months, average sized baby 2 years, small sized baby up to 33 months (2y, 9m).
At this age you may then feel comfortable to use a seat like Britax Evolva, which is a relatively lightweight, forward facing harnessed seat which turns into a highbacked booster later on. Or if it turns out your child is a giant and/or you are dead set on rear facing for as long as possible, you can get a lightweight 25kg seat such as Britax Two Way Elite, or Cozy n Safe Hudson for forward facing. If baby is average size or smaller, you could get the cheapest possible decent toddler seat (e.g. Joie Tilt for RF, Britax Eclipse for FF, which is also flight approved, so useful to have) and then once DC is 15kg and at least 3 and you're happy with them in a seatbelt, move whenever it's more convenient into Britax Adventure which is a very lightweight, low cost (but safe) high backed booster seat, or Maxi Cosi Rodi which has the advantage of coming apart to store, or max out the toddler seat and then use Bubble Bum, which is an inflatable one that goes incredibly small.
Total cost for Joie Juva, Joie Tilt/Britax Eclipse + Britax Adventure/Bubble bum = ~£150.
Total cost for Joie Juva + Britax Evolva/Cozy n Safe Hudson = £125
Total cost for Joie Juva + Britax TWE + Maxi Cosi Rodi/Bubble bum = £230
Add £20 if you go for the Gemm which has pushchair compatability instead of the Juva. And none of these seats are unsafe ones, although Bubble Bum doesn't really offer any protection.
The Dualfix and Joie 360 seats are both brilliant seats, but a massive pain in the arse to move from car to car because they are heavy and bulky and awkward. You need two hands to carry them - there is absolutely no way you could carry a baby or toddler at the same time. Can your relatives always park directly outside your front door? I struggle to carry ours any longer than a few paces - when we did a test drive, I wheeled it around on the pram! That worked because DH was there to look after DS2. If you needed to take public transport one way and be picked up the other way, this would be extremely impractical too. And disturbing the sleeping baby is a huge one - now we have a car, we can choose to simply stay in the car and wait if DS2 is asleep when we arrive somewhere. This isn't an option when it's somebody else's car if they need to get off somewhere else.
Another issue is that these seats are outgrown before age 3 if your child is 98th centile or higher, by around 3.5 years if your child is 75th centile or higher, around about age 4 for 50th centile. If you aren't comfortable with moving to a high backed booster with only a seatbelt at this age, then you'll be forced to buy another expensive seat which goes up to 25kg, for rear facing at least £160 or forward facing £80 (and they don't fit in older cars). It can make sense to buy an infant carrier and then wait and see whether you can get away with a cheaper seat up to 18kg (from £70 RF, £60 FF) or need a 25kg one and therefore buy it straight away.
IME, isofix is only faster for Group 1 only/Group 123 seats, seatbelt fitting is not very difficult at all once you've done it once or twice, especially now there are fitting videos on Youtube which we defo didn't have the luxury of back in the day :) I actually find isofix fitting a spin seat can be a bit more of a faff because you have to climb right into the footwell of the car and make sure it's lined up to click both sides into place and then sort the leg - seatbelt fitting takes seconds and I'm generally not sweating when I've finished doing it.
Sorry I know that's a bit of an info dump. If it was going to be the same car you'd use every time and you can keep the car seat in close proximity to the car, then I'd agree that the seats you've chosen would work, but for most non drivers in your situation they won't be the best choice.