I think you need to accept that you have put yourself into this position by choosing to rent from family members that you don't like.
You've said that you can't move somewhere else because you can't afford it, which is understandable, but that situation seems unlikely to change. You've now got two large, expensive pedigree dogs, so your monthly outgoings will now be even higher and will make renting elsewhere even less affordable - plus, a lot of landlords won't take tenants with one small dog, let alone two large ones, so you've made it a bit more difficult to get away.
So I think you're stuck in your current property for a while, and while you are living right opposite family members you don't like, you are always going to find it hard to avoid them, so all you can do is make the best of it.
I appreciate it's annoying that your niece and nephew are turning up unannounced with their mates, and I think you do need to be firm and say that it's not convenient when they do this and that you need a phone call first so you can tell them whether it is or isn't OK for them to come round. As you say, the novelty will probably wear off soon.
Regarding your BIL, does it really matter that he wants to take your dogs out? Malamutes need a good hour a day of exercise and lots of company, stimulation and stuff to do, so although I appreciate it's annoying that your in-laws are more interested in your dogs than you and your daughter, perhaps try to look on the bright side of it and see the advantages of having someone who likes to come round and play with them or take them out - at least for now. :)