I'm amazed you managed 2.5 hours, the first night we tried with our 2 (2y10m & 5y2m) we lasted about 5 minutes! This was about 4 weeks ago, it took a good 5/6 tries over 2 weeks - not every night so they didn't get into the routine of misbehaving and then the eldest being marched back to his room! We're 2 weeks in now and it's ok, they can be a bit rowdy but they both stay in their beds now rather than getting into each others. But, mine really want to share a room, so they're invested in it working out, so if yours aren't invested then there's no direct consequences of them misbehaving so that does make it harder for you.
My 5yr old and 2yr old share a bedroom and they have since my youngest was 6months old. The 2yr old goes to bed first, then 30-45 minutes later the 5yr old goes to bed and it works fine ☺️
Put them in bed at different times. Youngest first then the oldest. Could be just 30 min apart but then they are not being distracted by each other.