Are there any trading platforms designed to trade multiple accounts ?

Of course, there are such, you just need to look good.

I don't see much point in it, I think it's much more logical to keep the money in several different companies - so it would be much safer, and if you keep all the money in one place but in different accounts, it doesn't make any sense at all.

Of course, there is, and you need to choose the best option for yourself.

Now, in principle, you can find such an option, if you really need it