Edinburgh South West MP Joanna Cherry and Edinburgh East representative Tommy Sheppard have both announced they will not take part in the contest to replace Angus Robertson.
Ms Cherry, the SNP home affairs spokeswoman, believes she can “best further the cause of independence in my current role”.
It now looks increasingly likely the contest will be a two-horse race between MSP James Dornan and party member Julie Hepburn, who is not an elected politician.
Mr Sheppard had been widely expected to stand after competing against Mr Robertson in the previous contest, but said he wanted a more active role in formulating policy.
The party is looking for a new depute leader after Mr Robertson quit the role eight months after losing his Moray seat in the 2017 general election.
MPs Pete Wishart and the party’s Westminster leader Ian Blackford have already ruled themselves out for the post.
Ms Cherry said she had received support to stand, but had decided against it.
“Huge thanks to all across the indy movement who’ve asked me to stand for @the SNP depute leader,” she said on social media. “After long & careful consideration I’ve decided that, for now, I can best further the cause of independence in my current role.”
Mr Sheppard said the depute role is more about how policy is made rather than its content.
“I want to be to free to contribute and lead debates about the policy we should advocate and that’s harder if you’re running the policy-making machinery,” he told the Sunday Herald.
“And I think we’ve had some success here. On fracking, the National Investment Bank and other policy areas, we’ve seen grassroots policy working its way through branches and conference to end up as party and government policy.
“I intend to continue to work with others to similarly shape our future policy agenda.”
Mr Dornan, MSP for Glasgow Cathcart, was the first to announce he was seeking the post, with Ms Hepburn announcing her bid last month.
Ms Hepburn is not in elected office, but she is well known within the party and has worked for senior politicians. She is married to Scottish Government employability minister Jamie Hepburn.
Mr Wishart said that after taking soundings from colleagues, he did not believe he had “sufficient support” to stand for the post and Mr Blackford said he wanted to concentrate on his constituency and his role as SNP Westminster leader.