That is why I am looking for feedback and advice on how to best invest our money so we can have a secure retirement (together).
The information provided does not help us to help you because we don't know what percentage of the total assets the $75k represents.
However, you already know how to spread a portfolio out over several different accounts. Just add one more account (a rollover IRA) into the mix and fill it with something simple since it will not be getting more contributions. Maybe a bond fund - then adjust the rest of the joint portfolio for the stock to bond ratio that you jointly agree on.
If he wants his money separate, fill His Rollover IRA with a target retirement fund that has the appropriate stock to bond ratio (ignore the date in the name). Or use the lifestrategy fund with the closest stock to bond ratio. Or use Wellington plus some international if you want.
If you prefer using Vanguard's Total International in your SEP, just exchange to it. There is no reason to keep VEU if it is not your preferred fund.
The elephant in the room is "what about his new 401k?" It should also be thrown into this mix, but I don't think you have mentioned what is happening there.
It's a bit curious that you are asking your question about what to do with the money. You already know how to do this. You know how to do it well as evidenced by your own investments. Why is this $75k throwing you for a loop? Just do the same thing you would do if you suddenly discovered a long lost rollover IRA that belongs to you.
If there is some reason to keep his and her money separate, just do whatever you would do if the money were yours.