Based on everything I have read, seals are yours and go with you when you switch guilds. You are limited to 1500 seals a week unless you buy more. Any seals earned in one guild would not help the next guild. This means that if you switch guilds mid week after earning some seals you will not be able to contribute full amount to the new guild.
The devs were very focused on making sure switching guild could not be used as a loophole to allow an individual to get more resources.
It appears I need to learn to type faster on mobile