To neuter or not to neuter...

I have two dogs, both about a year old (exact age unknown since they're rescues), and I'm not sure if I should neuter or not. I live in the Dominican Republic where people as a whole don't much care for dog health. There are very little vets avaliable, even fewer with actual degrees, so there aren't a lot of places to get a trustworthy opinion.

Like mentioned, both of my dogs are about a year old. I have a Boxer/German Shepherd (James Bond or JB) mix and a Rottie (Cooper), both boys. They get along great, haven't had much trouble with fights for dominance or anything between them. They are guard dogs and due to some annoying people on my block, really really don't like men until they get to know them. They don't bark as much at girls. JB is a tad bit aggressive with food, but nothing major.

They have recently starting marking (ugggggg!) and I wake up every morning to my car tires squirted on. Will neutering help with this? What are the benefits to neutering? Is it absolutely necessary or will they do okay without it? Are they already to old?

No it's not absolutely necessary and no they are not too old. It's not a magic cure all either, if a dog marks pre castration he'll most likely continue to mark post castration.
I'm not a fan of neutering tbh and it certainly doesn't replace training. It stops procreation and that's about it. You could train your dogs to pee in a specific place if peeing up your car tyres is such an issue. Most dogs will pee up anything tbh a post, a tree, a table leg, a wall they ain't fussy.

As above - not a fan of neutering/spaying dogs for various reasons. The marking as Trouble said is likely to be a learned behaviour now but can be corrected with training ��

Neutering of male dogs is not a necessity in my view. As has been said, the only certainty with neutering is that the dog will no longer be able to reproduce. Socialisation, habituation, handling, training and management are the basis for having a well behaved dog.

With two entire males you may see a change in their behaviour towards one another as they mature - or you may not.

If your dogs urinating on your car bothers you then you need to teach them to pee elsewhere (there are various videos on youtube on how best to do this by reinforcement through repetition and reward). However, if they are guard dogs, are they outside alone much of the time alone? If so, it will take longer to consistently get the behaviour you are teaching.