Hi there, Anna,
I'm sorry your husband may not be able to join you for your first day at the Disneyland Resort. But any days together at The Happiest Place on Earth are better than no days together, am I right?
Regarding entering the theme parks together or separately, my answer is simply hakuna matata! It means, "No worries!" Even if everyone in your party has theme park reservations booked together, it's OK if not everyone shows up at the same time. If a member of your party won't be able to use their multi-day ticket on a day that others in the party use their tickets, that is also OK. That person may either forfeit that day, which may make sense if the ticket combination makes the overall ticket purchase more cost-effective, or they may choose to use that remaining day another time within the expiration window of their ticket.
A Guest who wishes to visit a theme park on a different day than what was originally booked with their theme park ticket may visit the My Theme Park Reservations page and choose the "Modify Reservation" link for the day they wish to update. If more than one Guest is associated with that same park reservation, the system will allow the selection of just the one Guest who would like their reservation updated. The other Guests will keep their existing reservations intact. Most regular theme park tickets will expire when all days of the ticket have been used, or thirteen days after the first day of the ticket has been used, or when the listed overall expiration date of the ticket has passed, whichever comes first. Although I would hope this doesn't apply to you, a wholly unused ticket that has expired may be upgraded or modified to a current ticket, which may require paying the difference between the original price of the ticket and the price of the new ticket type. Once a ticket has been used by a Guest, that ticket may not be transferred to another Guest.
Tony's Tip: Just as Guests booked together on the same theme park reservation need not enter the park together, Guests with separately booked reservations may also choose to enter the parks together. That is to say, not everyone in the same party needs to have purchased their tickets and booked park reservations at the same time. Also, multi-day theme park tickets need not be used on contiguous days. You seem to have already done the math for your particular travel plans. So this may not apply to you. But I'll put it out there, just in case the dates you plan to visit the Disneyland Resort line up with one of the dates of a lower-tier date for 1-day tickets. In some cases, it may be cost-effective for a Guest to purchase a single 1-day ticket for use on a low-tier date during their visit and use another multi-day ticket for the other days around that 1-day ticket date. This savings hack may be particularly helpful when the multi-day ticket is a special offer ticket or otherwise purchased at a special discounted price.
I hope you have a magical time at the Disneyland Resort, Anna. Please stop by planDisney again for any advice and recommendations we may be able to offer you.
TTFN! Ta-ta for now, Anna!
~Tony