Well I have the same situation I have 6 accounts with unique proxies to each so this is what I do
I open the first client and I wait so it loads on osbot then I opend quick the other 2 clients (you have to be quick when you open both vanilla clients) and you'll have your 3 first clients opened
And for the other 3 I do the same but this time I open everything but in SandBoxie.
I hope you understood and it works for you