Boston would be your best target race and if the weather isn't right, you can use it as a hard training run and practice whatever you need to during the race. Then gear up for Grandma's marathon to end your training cycle. Rest up, and build back up again if needed for a fall/winter attempt at an OTQ.
If you end up racing Grandma's, you mentioned you have 4 weeks less of training for CIM as a last ditch effort. Well, if you plan to run something last minute and just want to get into the trials, perhaps you can race Houston instead of CIM as a complete last ditch effort. Get an extra 4 weeks and just pray you have enough left to run a decent time at the Trials come February. Good Luck! I'll be doing Boston this (2019) year and looking for an OTQ. But, you could do something like this:
Spring
Boston (main spring race)
Grandma's (back-up)
Fall/winter
Chicago (main fall race)
CIM/Houston (back-up)
Also, i'm guessing if you have a 2:25 or faster, you might get into the top seed with the elites, you would just have a low number and not your name on the bib.