Keane has been the England U16 men's head coach for the past five years and he currently operates as the assistant coach of the NBL Division One club Reading Rockets and the U15 and U13 London Regional boys' teams. He is a director at the Lampton School Basketball Academy.
"It's an absolute honour and a privilege to be appointed the Great Britain U18 head coach. Working with the best junior players and coaches in Great Britain for the first time as Great Britain is something I will truly cherish," Keane commented.
"The pride to lead England in the past and Great Britain now keeps my mind ticking every day with regards to how we can be better as a team; as a staff; as a programme and - ultimately - as a nation.
"I want nothing more than to see this group of players move through the ranks, represent GB seniors at the highest level and take our game to new heights."
Following a distinguished playing career for club and country, Commonwealth Games gold medallist Ellis is currently the assistant coach of the GB senior women's team, the head coach of the England U18 women's team and a coach at the Sheffield Hatters Basketball Club.
She has previously served as the head coach of the GB U20 women's team (2006-2008) and the assistant coach of the England women's team (2001-2005). Ellis was the director and head coach at the All Saints Basketball Academy for three years (2012-2015) as well.
"I take great pride in representing my country and feel honoured to be the first Great Britain U18 women's coach," Ellis said.
"I'd initially like to establish an excellent training environment that enables the athletes to improve - both individually and as a team, instil a great team ethos and get everyone on board to work towards a common goal.
"Ultimately though, I just want to be part of a team of people who are helping to make positive changes in the national team environment and develop a culture in training and playing that will improve the women's game - both domestically and internationally."
Having begun his coaching career as the England U18 women's assistant coach/team manager, Vear held a number of club and regional roles across Kent and the South East before gaining further experience overseas in Canada (Dalhousie University) and Denmark (Aalborg Basketball Club).
He has since returned to these shores, where he is now the head coach at the Barking Abbey Basketball Academy and NBL Division Two outfit Kent Crusaders, as well as the lead assistant coach to the GB men's U20 team.
"I've always believed coaching at national level to be the greatest honour that can be bestowed upon us as coaches," Vear stated.
"I'm equally grateful to have inherited a great programme from Alan Keane, who has set a culture and standard that is among the best in Great Britain at any level.
"It's now time for me to build on Alan's success and I'm excited to have the opportunity to put my own stamp on the team and programme going forward.
"My first priority is to ensure our players develop over the next three months in preparation for April's training camp.
"Communication between our GB coaching staff, the players and their academy/club coaches is key, with a shared goal of promotion to Division A this summer."
Harber has been the women's basketball head coach at Loughborough University since 2009 and the Women's British Basketball League (WBBL) club Leicester Riders for the past six years.
He has also worked with the England U15 girls (Head coach), U16 girls (Assistant coach), U17 girls (Head coach), the 3x3 senior women (Team leader) and the GB U20 women's (Assistant coach) teams.
"I feel extremely privileged to have been appointed in this position and I know that I have a great opportunity to influence the next generation of British players for the future of the women's game," Harber said.
"We have a lot of challenges within our basketball landscape, but I'm confident that - with a collaborative approach between all of the stakeholders within British basketball - we can create a positive environment for the youth national teams.
"For me, it's about establishing standards and expectations for what it requires to wear the Great Britain jersey and create a positive environment that people want to be involved with and initiate the U16 programme on the right way and in a positive, strong direction."
Basketball England CEO Stewart Kellett said: "We have the utmost confidence that these four appointments are the right ones to propel British basketball towards an even better and brighter future.
"Alan, James, Matt and Vanessa possess the necessary coaching credentials to bring about the change in fortunes that we all want to see at these two pivotal age groups, which can only be of benefit to the senior team going forward."
Interim Chairman of the British Basketball Federation (BBF) Bill McInnes congratulated Alan, James, Matt and Vanessa on their respective appointments, adding: "By working together, the BBF and the Home Country Associations can recruit, retain and develop high-quality coaches for all GB teams. This is evident by the quality of these appointments."
Barry Lang, Head of Basketball at Basketball Scotland, commented: "It's great to see progress with the GB youth teams and we are looking forward to working with the talented coaching staff throughout the programme.
"This first-time merger of youth national squads provides all of the home nations an excellent opportunity to share best practice and we look forward to our Scottish national team coaches being involved in this exciting environment, where they will learn and be able to share this knowledge with the Scottish basketball community."
Basketball Wales' Performance Director Cameroon Seeley said: "Basketball Wales is pleased to have been involved in the recruitment process of all the newly-appointed GB youth team coaches.
"We wish each of the coaches and their respective teams the best of luck in the FIBA tournaments this coming summer.
"All of the Basketball Wales national team performance coaches and staff are looking forward to working closely alongside the GB coaching staff in the future in order to develop our knowledge and skills and to fully contribute to the GB coaching and player pathway."