I’m having a hard time opening side-by-side terminals

Side-by-side how? the way I imagine this is starting with a single window with a regular buffer, then opening two toggleterm terminals in splits to end up like this:

If that's what you mean, all you need is to pass unique terminal ids as you call ToggleTerm.

• :ToggleTerm 1<CR>
• :ToggleTerm 2<CR>

You could then map that to whatever keys you want, like <c-1> and <c-2>:

vim.keymap.set('n', '<c-1>', ':ToggleTerm 1<CR>')
vim.keymap.set('n', '<c-2>', ':ToggleTerm 2<CR>')

I have a similar setup: https://github.com/davidmh/dot-files/blob/3b0e79919f231db1f3628f6fde06e9f78f347b87/nvim/fnl/own/plugin/toggle-term.fnl

• ctrl + 1-5 for dedicated split terms
• alt + 1-5 for dedicated tab terms
• ctrl + t as a wildcard split term, that's my go to
• alt + t to attach or start a tmux session in a tab