With regard to your dogs, it's worth remembering that your will might not be looked at by anyone until quite some time after your death. So it would be best to ensure suitable provision for them in a different manner.
My cats are signed up with the Cat Guardian scheme and I also subscribe to the Cinnamon Trust. You might want to look into the Dogs Trust Canine Care Card or the Blue Cross Pets into Care Scheme:
https://www.theralphsite.com/index.php?idPage=77
(As an aside, I'll mention that the Cinnamon Trust also tries to provide dog walkers for people who're still alive but who can no longer walk their dogs).
With regard to your will though, there are no rules. My own instinct (and the way that my own will is worded) would be to go mainly or wholly with percentages. That way, if the value of your estate changes a lot (e.g. because you have to use some your share in the house to pay care home fees), it will still be simple for your executors to work out who should get what.