Is 1031 exchanges even done if I only have the ownership for a short time? 

So no, you can't force them into using a new automatic payment process.However, you can incentivize them...There's nothing stopping you from offering the tenants something of value to them in exchange for signing an amendment to their existing lease that requires rents to be paid as you prefer.

Would that still not be exchangeable?

If he will have a gain (i.e. proceeds in excess of basis) there are ways for him to defer or exclude this gain in the year of sale.Gain on sale of residences may be excluded from income.1031 exchange and QOZ may allow him to defer the income to a later year.Engage a tax professional as there are many details that need to be worked out in order to qualify for any deferral or exclusion transaction.

I think young professionals will continue to pay the high city rents in exchange for convenience and better quality of life. 

Got a few tips to exchange.

You can try a 1031 exchange to avoid the capitol gains. 

If he sells and uses the proceeds as a 1031 exchange, can we both go into a purchase together as in mortgage/deed?

I will file a 1031 exchange with all the properties.

@Isaiah WrightI haven't done a seller financed deal yet, but I've been doing obsessive research in the past couple weeks.This pros of this purchasing strategy are that the terms are negotiable, and you can get away with putting low or no money down in exchange for a favorable interest rate and sale price to the owner.