Does anyone know if you complete an Ambition and start another one, will you lose the earned perk?
Is it possible to earn more than one perk by completing ambitions?
You keep whatever you achieved by completing an ambition. You can switch between ambitions throughout the game play and complete them incrementally.
Thank you so much! I’m really happy to know that. It took a long time to get the Loving Family one, and the mom who earned it is aiming to become a grandmother. So becoming a Parenting Expert will be very easy for her when the parents are out working. 
Glad to know 
You can change the key influencing value of the zoi by choosing the correct conversation options with others (like family members in this case) and by fulfilling some urges and not fulfilling other urges that could be counter-productive to your goal/ambition. The values help in getting the ambition achievement sooner by speeding up improving the relevant skills.