ERF disagreement

[Ataner]

Good evening, long story short my 3.5 year old is still rear facing which my husband is happy about. However for a while he has hinted that she shouldn't be RF much longer and we need to pass her car seat onto her brother soon. I would like to keep her rear facing but my husband thinks car seats that RF beyond two years are a pain to get in and out of the car, plus we would need three of them (our car, my parents and his parents) and they are expensive. Also, his mum's car is quite small so I'm not even sure it's an option.
Apparently my daughter has said she's uncomfortable in my MIL's RF car seat. I've said I'm less worried about his mum's car as she only does two journeys a week which are all off peak and 30mph. However this has lead to us disagreeing about what to do in our car, and even though she'll be nearly 4 when we move her brother into her current car seat I'm anxious about her no longer RF and it has lead to an argument that I can't see us getting over.
My husband has in theory given in but said I'll have to do the research, buy the car seats and install them and I'm just feeling like absolute crap about disagreeing about something important like this.
Do I give in and forward face at 4? Or let him give in and spend a fortune on 3 car seats which are less convenient and will need replacing again in a couple of years?

Re space - of there's space to FF then there's space for something like a minikid (theres a certain amount if space you need in a crash to stop you from bashing your head against the seat in front. I have even fitted one in a suzuki splash which is the same size as a little tikes car lol.

If i were you i would just get the seats you want. Something like a minikid you can transfer between cars anyway in a minute or two (but you need the tethers installed in each car).

I find RF handy as i often squeeze into small car park spaces so i only need the doot open a crack to plug them in vs much wider if i am leaning further for FF.

Thank you, unfortunately transferring between cars is not an option as sometimes my MIL will unexpectedly have to do nursery pick up so she needs to have her own, and my parents live in Spain so also need a separate one. My husband has agreed to continue RF but he's angry at me for pushing it so much and "acting like I'm superior". I wish I could let go but it gives me so much anxiety thinking of having an accident while forward facing and knowing there were safer options that we didn't go with.

Britax max safe pros are an excellent ERF seat and are currently on sale for £189 in loads of places. We've just bought one for our 3yo for grandparents car and she said its super comfy. It goes to 36kg / 125cm as well so you should get plenty of use out of it and the sides are low so DD1 basically climbs in and out of it herself.