I want to apologise somewhat for this all, I went down getting an engine because I wanted an Aston Martin engine. Similarly, I get sister teams not for success, but in getting them (and usually not caring too much about them) I can have more of my favourite drivers then ever, and a side effect is that it keeps the grid closer to full, keeping interest for all parties.
Tobi approached me before the season asking if I wanted to get engines off him, I told him not to worry as I'll be getting one for myself. We discussed sister teams briefly, it wasn't important.
I went with my third team because again, I wanted the idea of having extra drivers, Tobi got his sister team, it's all going well. Obviously to some people seeing 5 teams with an engine instantly becomes a bad look, it shouldn't have been.
In the end, me and Tobi are both proud people and what we saw was a poorly thought out challenge to what we stood for. We didn't mean to break the game, but we felt that if we didn't act, we would be unfairly left behind. So I acted. Aaron and Nathan were only too happy to help out.
All of the suggestions so far seem silly, keep everything the same and restrict only custom engines to 2 engine upgrades per market. Not teams, the entire engine manufacturer. Problem solved.