Yes you can write your own contracts. A written contract is only a written record of something that has already been agreed in speech. So to start with write down in simple terms what has been agreed already, that is a good starting point.
5 Ways to Begin Creating Shared Agreements Everyone participates. Cultivate a safe space to speak from the heart, but be open to feedback when your words harm others. Listen from the heart. Make sure that your intent matches your impact. Lead with empathy and self-awareness. Listen to understand, not to respond.
The biggest difference is that an SPA is the sale of all shares, and an APA is the sale of selected assets. Therefore, they are both different transactions and have different procedures.