Money is changing hands (assuming monetization of course), you're both in separate countries, there's no clear authority as to who is in charge, there's no expectation of who is responsible for what nor to what degree. There's no exist plan in place. One of you might get sick of doing this, but the other is 120% in all the way. How does the disinterested party end the business relationship?
Let's say the channel takes off, you get a million subscribers and 10 million views. You're doing 95% of the work. They're riding on easy street. Who deserves what percentage of the YouTube royalty check? How much resentment will build when you're carrying all the weight?
Friends often make the worst business partners. Never inter a business relationship unless you have a minimum of 51% control. Maybe you are not thinking of it as a business, but if money will change hands, and you're dealing with international law, then you need some kind of contract that lays out what each of you expects from the other. Do all this up front and everything laid out on the table. This isn't some hey-let's-get-pizza-this-Friday-night. More friendships have been ruined because of business partnerships. You're setting yourself up for a miserable time. If you want to do this, then you will need to outline all this up front. What you're talking about is a kind of marriage even though you're just talking about a YouTube channel together.
Something like this cannot be answered via an online forum, you need professional advice. If you don't know why you need a lawyer, then you really need a professional to help you navigate these sorts of potential problems.
In my honest opinion, you need to have your own YouTube channel, they need to have their own YouTube Channel, then you collaborate as often or a little as each of you desire. Each of you retains 100% control over your own enterprise. There's no expectation as to who is responsible for what. Save yourself a world of nightmare and headache.
