Do I need to Have One Landing Page or Two – For two products, services or even companies

Many of our clients face such a dilemma: how to promote equally effectively two products/services/companies at once. We have been asked various questions:

1. Can I use one landing page for two products?

2. Do I need two landing pages for two products?

3. Can I make one website for two companies?

4. If I have two services, do I need two websites?