Hi Daniela
You say you have a high rebate card - expiring in a few weeks, and so you seem to want to spend something on that... well I sorta get that. But I would advise, only spend money if you really need / highly want photographic gear/items, not just to 'use money'. (I am planning to get the R5 also, though probably when the first 'deals' on it come available).
As you stated you will use the camera for hiking and family photos. So, if you want a native RF normal zoom, maybe go for the RF 24-105mm f/4 which already has very pro and good user reviews with the EOS R and RP. (Imho, the 24-105mm f/4 is more versatile than the 24-70mm f/2.8 or the 28-70mm f/2 - the latter of which in particular, is more of a specialist lens option).
If I were in your shoes (which I know I'm not), I advise you stick with lighter options so you are more likely to take them hiking. (As much as there is a place for brighter lenses)... So for wide angle, potentially keep the EF 16-35m f/4 you have... as that's already a great lens. The 15-35mm f/2.8 is larger/ heaver / more expensive, while being just a smidge sharper than the ultrawide you already have, but for all practical purposes, they'll produce almost identical images. (I have compared on various websites and in actual images). Ok, you do get 1 extra mm, and 1 stop with the RF 15-35mm, but you are paying for that in weight (and size/cost). So, unless you do event photography, I'd stick with the 16-35mm f/4.
I like IS in lenses - and with the R5 having IBIS too, best of both worlds. You wrote you are already planning to get the RF 70-200mm f/2.8, which is a great lens from all accounts. That makes sense as a telephoto for this body. (I have the 70-300mm L, and plan to keep that. However I will also definitely try the 100-500mm f/4-7.1 lens, which actually interests me a lot, as I do a fair bit of wildlife, and don't need a super fast lens).
So, my advice as to 'what lens to get' is to think about buying a prime, if you really feel like you want/need an addition to listed above. The first one that comes to mind is the 35mm f/1.8 STM IS (which can be used as a handy little prime and macro for certain situations when hiking). I can see me using my 100mm L IS USM n the R5 a lot (with the RF-EF adapter). So the 100mm L macro might be another lens option / consideration for you, even though it's not an RF... but it will work great with the RF-EF adapter, I've used it on the R, and it's really great!
The other primes you might want to consider are the RF 50mm f/1.2 or the RF 85mm f/1.2, but these are again quite specialist lenses (big / heavy / expensive, but great optical quality). So you might want to consider the 50mm f/1.8 STM (a surprising good lens, and with IBIS in the R5, it'll will work a treat in low light!)
I trust this helps.
Paul