They are selling because don't want to continue self-managing it and their kids are growing up so they don't use it as often.I've been thinking making a couple offers, with one including "2 weeks free rental per year for the next 5 years" or something like, thinking that it might be meaningful to them to be able to continue to enjoy the place without the hassles of owning it.If we did that then we of course have to account for what happens if we sell the place or are living in it, in which case we would just "refund" them the weeks' rent.Forgetting about making the pricing rationale and whether they would or wouldn't want it, has anyone figured out the legalities or contract language for doing something like this?

A custodian can certainly have a meaningful impact on fees, the types of investments allowed, and the speed with which you can transact.

How are you finding deals, and what are you doing to extract the maximum profit from your flips?

It's important and meaningful. 

My active investments (which require work and time), I typically achieve returns in a different stratosphere than 3.5% (most of my RE investments are infinite return as they have had all investment extracted). 

It's part of your job to extract this information from investors, and since many don't know how to really communicate this, we do mean extract.Suggest you also NEVER forget to put a price on your time!

Then ask what it's worth for them.There's no time for them to accrue any meaningful amount in that time span if charging purely interest. 

They want it to be a "meaningful" amount to each individual.

Cash-on-cash is much more meaningful.

Such as, clever things that you've learned to save time, extract lead nuggets out of half a million old emails, best mail merge techniques (which Thunderbird might do, we'll see) etc.