My elder dog keeps shaking whenever he’s laying down

Hi I’m sorry, I don’t know how to put this together because I’m like on the verge of crying but my dog, Max, he’s about 15 years old. He’s a lab and pug mix I believe and I say about for his age because we don’t know how old he was when we got him from some random couple but the vet said he was about eight when we got him, so he’s super old.

Recently I’ve noticed him limping a lot in the front half of himself, which is where I also notice the shaking, like whenever he’s laying down both front legs just shake like he’s cold, so at first I thought he was cold so I kept trying to warm him up but it happens even in a warm area. Also I’ve noticed the whites of his eyes are red too. I’m worried to ask my dad to take him to the vet because we’ve been having money issues and I’m worried my dad will just say “oh he’s getting old that’s normal” or something like that. I don’t know, I’m just scared because Max has been my best friend since I was six and I don’t want him to be in any pain.