Smith (21) and Crosswell (24) join Canterbury first five-eighth Colin Slade (22) as confirmed signings for the franchise for next year.
Joseph said Smith was a promising halfback who had a good temperament and showed he could rise to the occasion.
Smith, a trained hairdresser, was a member of the wider training group with the Blues this year, and played under Joseph for New Zealand Maori.
"He has a different game to Jimmy Cowan and can attack and threaten around the ruck and maul. He has got a good head on his shoulders," Joseph said.
"He really impressed on the Maori tour, just with the way he handled the step up. Sometimes there can be a question mark over young players and whether they can be all right at the next level but he was fine."
Crosswell, Manawatu's captain, played for the Hurricanes last season but received limited game time.
Joseph said Crosswell was a big, abrasive forward who was a good defender. A sore knee was keeping him off the field, and he had sustained a few injuries in his career, but injuries affected most forwards in the modern game, Joseph said.
The Highlanders coach was talking to other players and more announcements would be made next week.
"We're still talking to players around the traps who are available and have the attributes and characters that we are looking for."
Other names bandied about include Wellington midfielder Shaun Treeby and Taranaki loose forward Jarrad Hoeata, but Joseph said nothing had been signed yet.
With franchise contracting coming into force this season, it was important to get in and sign players before other teams got hold of them, he said.
The draft will in effect be non-existent, as sides look to fill all gaps in their squads as quickly as possible.
Slade signed earlier this week, in a big boost for the franchise.
Joseph said most of the Highlanders would come from the South but it was important to get players under contract early from other parts of the country.
As to the future of Otago loose forward Adam Thomson, who is being pursued by the Crusaders, the ball was in his court, Joseph said.
"There is not a deadline for him to make the decision but it would be best for him to make the decision and get it out of his mind and focus on something else."
Joseph said his 32-strong squad for the 2011 season would include three halfbacks and three hookers.
"You've got to have those specialists because if one of them goes down, then the next one off the rank will be straight into the 22. But just because we have picked Aaron [Smith], that does not mean he is going to be our No 2 halfback. He is just someone in the mix who we think can do a job for us and it prevents him going to another franchise."
