The Portuguese said the same last season, but they finished third.
Kiernan moved for an undisclosed fee, while Forrester is not in the squad.
But Caixinha said: "I always think that, when I'm working at a club, my players are the best, my squad is the best and my club is the best."
The 46-year-old, previously in charge of Al-Gharafa in Qatar, has been busy in the summer transfer market, with nine players added to his first-team squad and 10 heading in the other direction.
Kiernan joined Southend, in League One, on a three-year deal, and fellow Englishman Forrester were told by Caixinha at the end of last season that they would not be involved in his first-team plans.
"They are not with us since the very beginning and they knew that from me from the end of the last season," said Caixinha as he confirmed both players have been training with the club's under-20s.
"Rob's situation [has been] solved, but Harry may take a little bit longer.
"That's all I can tell you."
Meanwhile, Caixinha refused to discuss whether Jamie Walker would play a part at Ibrox this season.
The winger was left out of Hearts' squad by Ian Cathro before the head coach was sacked this week and interim boss repeated the claim that he was being left on the sidelines because the continued transfer speculation was beginning to affect his mental state.
Rangers were knocked out of the Europa League in the opening qualifying round by Luxembourg's Progres Niederkorn, but Caixinha continues to exude confidence in his team as they prepare for Sunday's opening Scottish Premiership fixture away to Motherwell.
"I need to represent it like that and I need to spread that feeling from bottom to top and top to bottom," he said.
Caixinha is taking heart from last week's friendly draw with Marseille and warm-up victories over Watford and Sheffield Wednesday after the disappointment of Europa League defeat.
"It was a long hangover, but it was a tremendous effort to look forward," he said.
"This is the best moment ever since I arrived. That shows the improvement and how pleased I am with the boys.
"The team that you may call the first XI has only been together for three weeks, so I have to be happy.
"In the last two-and-a-half weeks, we've had the best moments since I arrived - as a squad, as a team and as a working group."