You're hurting your conversion rate by loading FAQ in a new tab.
This way you are forcing users to go to another tab breaking their task flow. Elderly users may not even know that a new tab is opened because they, generally have low computer literacy. That makes the problem even worse.
A much better solution would be to place the FAQ at the page where the questions arise. This way you won't break their task flow, and provide needed information.
Don't worry about the clutter. If you open the FAQ in new tab you require much more mental workload than if its displayed in the page itself.
Trust is important
If users don't trust your site they won't put their personal data. There is a good article by NNgroup about trust and conversion rate.
Sites must meet users' basic trust needs before they demand that
visitors enter information or engage with them. The trust pyramid has
5 distinct levels of user commitment, each with separate design
requirements before users will give a website what it wants from them.
We currently have too little users to do a valuable user test, which
is why I'm looking for experiences or answers in this field.
You don't need user base or traffic to make a user test. You need this for A/B tests. To conduct a user test you should recruit target users (age 50+) and then give them tasks to complete while you watch them. Here is a good resource on this topic.