I-864 Joint Sponsor Past Tax returns

My spouse and I are currently looking into using a mutual friend as a joint sponsor. The mutual friend makes six figures and easily clears the poverty guidelines, however they only have two years of tax returns. Additionally, they have already sponsored one other person (their spouse). I see most people/sources say neither of these things are a big deal, but we are doing this as a response to a RFE and want to be as certain as possible before moving forward with them.

Does anyone else have any experience using a joint sponsor that didn't have 3 years of tax returns? Any experience using a joint sponsor, who's already sponsored someone else? I just want to be a careful as possible so we can avoid a rejection. Any help is appreciated!!