Hi, all of mine are with petplan and you do get multi pet discount (think it's £1 per month) The premium amount may differ though due to age of the new dog.
I've made claims too, and I must say that whilst you pay a lot for the premium (IMO), they are fantastic at paying out.
One of mine has Pyoderma (not sure of spelling) which is caused by allergies that affect the skin (his little body produces to much oil) and I claim for his immunotherapy injections (I do them once a month myself),his shampoo, ear cleaner - I think they even paid out for his teeth to be cleaned and some removed becaue the condition affected his gums too. Each year I pay for the excess on the policy and they pay everything else.
I cannot praise them enough (and I work in insurance myself)