They replace Paul Hudson, who has moved to the Saints, and Luke Beveridge.
Collingwood is still to announce a replacement for Gavin Brown, who spent 26 years as a player and coach at Collingwood, the last three as VFL coach.
Brown resigned last week to take up an assistant coaching position with Carlton.
McRae, who was the development coach at Richmond from 2006 to 2009 and spent 2010 working in a similar role at the Lions, will be the development manager, while Lappin, who has worked at the Blues for three years as an assistant coach, will fill the same role at the Magpies.
The Magpies' coaching panel is led by Mick Malthouse, with Nathan Buckley, Mark Neeld, Scott Watters and now Lappin as assistants.
McRae, a three-time premiership player at the Lions, said he was enthused by the opportunity to work at Collingwood.
"I'm really excited to come to a club that has set the benchmark, and I'm grateful for the opportunity to work under Mick in 2011 and Nathan beyond that,” McRae told collingwoodfc.com.au.
"I'm passionate about working in player development and looking forward to working closely with what is an impressive Collingwood playing list, and helping the club improve further."
Lappin, who played 251 AFL games for Carlton and St Kilda and was an All Australian in 2004, said it was a good time to be starting at the club, in the year that saw it win its first flag in 20 years.
"It's an exciting time at Collingwood, and to be given an opportunity to come in and help the club maintain its high standards and improve further is something I’m very appreciative of," Lappin said.
