I think I would send everyone to the parks early and do the check'in myself if we switched hotels. Then they get full park time and I get a few sanity minutes.

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That is a nice idea, but it might not quite work the way you are thinking. If you arrive at any hotel before 3pm, your room probably won't be ready. Sometimes it is, but I wouldn't count on it. the WWD ME bus (from MCO) drops you off at the hotel. From there you could split up, and they could get on a bus to the park.
When you arrive at US, more or less everyone has to stick around until you finish printing out your Express passes. I mean they could go to the parks without them, but those passes are one of the key perks of staying at a US deluxe. The cost of EP varies, but is worth a minimum of $85 per person, per day.
Further, if they plan to use the early entry hour, then they need to have/show their hotel room key. At check-in, the front desk issues hotel room keys for everyone in your party. You then insert your room key into a special kiosk, and follow the directions. The kiosk takes your picture, which gets printed on your personal pass.
Arrival to getting your pass only take s a few minutes, but everyone should stick around until they have their pass and hotel key in hand.
I thought I read somewhere that mears offers some sort of hotel switch service if you are coming or going between the 2.
Yes, the Mears transportation company offers a shuttle service between MCO and Universal. You can look up the rates for your specific hotels.
In some cases, that may be the best option, but there's a few things to consider: the shuttle charges a fee per person, so it might end up costing the same as a taxi.
The bigger drawback, IMO, is that the shuttle makes multiple stops until it is full, and each of those stops takes time. I've looked into it, but decided it wasn't for us.
I previously said we don't go crazy trying to arrive exactly at rope drop, but we do our best to arrive close to rope drop as much as possible because crowds and attraction lines quickly grow.
The Express passes are a big help, but you can still cover more ground when the crowds are lowest. Also, no Express Pass (EP) on HP.
I've priced the options a number of times. A rental car for a full week is usually under $200 for a mid size. A one-way sedan/taxi is about $50 (WDW to US, plus tip and bag fee), the shuttle (look to see what is offered) is about $20per adult, one-way. The ME bus is free from MCO to WDW, but it is slower than getting a rental car.