Continuous residence- travel every year for more than 6 monts

[Frdk2]

Trying to help parent apply. They have had green card for several years. >40 yrs. Have had multiple trips over last few years. On trip a year, 2 of those was more than 6mths, less than a year. What type of evidence would be sufficient? Tax returns not relevant as parent is retired and hasn't had to file. Had a lease during first two trips, but now listed as occupant under current address (lives with me). Has active utility bill first two trips, active bank account throughout, and addressed mail to his residence while he traveled. Wondering if this is enough to apply. Have consulted lawyers, 2 seems clueless about this and werent even aware of continuous residence requirement, and two others seem to think we have enough evidence (using active bank accounts)
Anyone with such multiple trips, retired, able to get citizenship?