Using two domains questions

Client wants a simple 2 page coaching site. Main homepage is for one audience, NOT LINKED homepage for another.

1. I can easily assign the Squarespace domain to the regular homepage, but would like to use Namecheap or GoDaddy secondary domain to link to the NOT LINKED homepage. Is this possible? I thought it was but this article seems to say it isn't:

2. Also, that secondary domain provider, how do I ensure that if a person types in https it will connect? Had a situation with Namecheap once where I had to buy hosting there to ensure the https version worked. Will Squarespace's SSL cover both domains?

Thanks!