From the Henri Coanda Bucharest-Otopeni airport, probably the best way to go to your hotel is by taxi (the taxi station is at the exit of the Arrivals terminal), especially if you are coming together with a few colleagues and you can share a taxi.
It is possible also to use the express bus no. 783, which goes from the airport to the city center (you will have to buy a magnetic card (ticket) and validate it in the bus). See more details at https://www.bucharestairports.ro/en/access and https://www.stbsa.ro/eng/route_timetable?783 at 2nd (Return) direction timetable.
If you go by bus 783, the nearest bus stop from H. Radisson Blu/H. Park Inn by Radisson is Piata Romana (at about 500-700 m). The bus stop closer to H. Novotel city centre is the next stop (Piata 21 Decembrie 1989), at about 400 m from this hotel. Depending on the hotel chosen for accommodation, some participants will have to get off the bus at the last stop, at Piata Unirii 1.
For transport in Bucharest, you can use car sharing systems, like Uber or Bolt.
Probably, the taxis are more cheap and you can order a taxi using a free application for Android/IoS called Star Taxi, https://www.startaxi.com/?lang=en
The web site of STB SA - the public transport company in Bucharest (tram, trolleybus, bus) is https://www.stbsa.ro/eng/index . The metro map: http://www.metrorex.ro/prima_pagina_p1352-1