Legality is rarely the obstacle
Texas law does not prohibit dividing cremated remains. What it does is put one person — the authorizing agent under § 711.002 — in charge of disposition. So the real question is whether that person agrees, and whether the rest of the family will accept the outcome.
Where a family is likely to divide, decide it before the cremation. Retrofitting a division onto a decision already made is where arguments start.
Ask the provider to do it
Most providers will divide remains into multiple containers as part of the arrangement, often for a small fee per additional container, and will do it in a controlled setting rather than a domestic one. The division is more even, nothing is lost, and no family member has to be the person holding the scoop.
Say how many portions and roughly what proportions when you arrange, not afterwards.
Keepsakes are a different product
Small keepsake urns, pendants and rings hold a token amount rather than a share. A family can have both: a main portion interred or kept, and several keepsakes. Those are ordinary retail items and can be bought anywhere, not only from the provider.
Write down who has what
A short note recording who received which portion, and when, prevents the awkward version of this conversation years later. It matters most where one portion is later interred or scattered and another is not.