The club are close to appointing the former Ajax and Inter Milan boss, 47, to succeed Sam Allardyce, who led Palace to 14th in the Premier League in May following a relegation battle.
"The Champions League is not realistic but with good organisation you can stay in the middle," De Boer said.
"With a great season, maybe you could sneak European football."
Between 2010 and 2016, De Boer coached Ajax, winning the Eredivisie for four consecutive seasons between 2011 and 2015.
But the former Netherlands international has been out of work since he was sacked by Inter Milan in November 2016 after only 85 days in charge.
"It's always been one of his desires to come to the Premier League," added Ronald.
"It's the biggest league in the world - not necessarily the best - but the most exciting for sure. Frank wants to be part of that and hopefully he gets that opportunity with Crystal Palace.
"As it stands now, I know that both sides want to go with each other but there are just little things to discuss."
De Boer was appointed as Inter boss two weeks before the start of the 2015-16 season after Roberto Mancini left by mutual consent.
He had never previously coached or played in Italy and led Inter to just four league wins in his opening 11 games, leaving them 12th in the Serie A table.
"Falling down on your face sometimes helps you to move forward," said his brother.
"It's so difficult to step into a team who are not at all fit and have an average age of 28, just two weeks before the start of the season. It is very difficult to change the philosophy.
"But he learned he needs a good pre-season to get a proper idea of what his squad is about.
"He is more than capable of doing well with any team and also with Crystal Palace if he decides to sign with them."

The "Total Blackout Tour" will see Rock head to Manchester, Leeds, Nottingham, Glasgow, Birmingham and London in January 2018.
His last tour in the UK, "No Apologies", saw two nights at the O2 Arena in London sell out.
The shows also broke a Guinness world record for the largest audience at a comedy show at the time.
"I have to say it was one of the best experiences of my career", Rock wrote on his website.
"The crowds were incredible. The people were smart and came to have a good time."
Rock began his career as a comedian and cast member on Saturday Night Live, and has also featured in films such as Madagascar and Grown Ups.
The first UK show will be in Manchester on 11 January, with Rock travelling to Glasgow to play the SSE Hydro on 24 January.
Frank de Boer could help Crystal Palace to the Europa League if he takes charge at Selhurst Park, says brother Ronald.
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Comedian Chris Rock will play a show in Glasgow as part of his first UK tour in 10 years.