Lyra can be exactly this - a feed for close friends and family. Just make a group with them in, and set your Conversations feed to show just that group.
We have extensive experience with AWS (where Lyra runs) and we're confident that we can keep running at the price point we've set.
Because we don't intend to take any investment, our plan is to become sustainable. We don't have an exit strategy and we don't intend to sell. As long as our users are willing to subscribe, so that we can pay our engineers and cover our running costs, then Lyra is here to stay.