Is roaming free in Bulgaria for our group if we have UK or US SIM cards?

That depends on where your home SIM cards are from! Since Bulgaria is in the EU, the "Roam Like at Home" policy generally applies to EU citizens. However, if your group members are from the UK (Post-Brexit), most UK carriers (like O2, Vodafone, Three) have reintroduced daily roaming fees, typically £2-£6 per day. For travelers from the US, expect standard international roaming charges from carriers like AT&T or T-Mobile, which can be quite expensive. Triply offers a straightforward, single plan for everyone to avoid these varied and often high costs.